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How Haiti Was Devastated by Two Natural Disasters in Three Days

By Tim Wallace Ashley Wu and Jugal K. Patel Aug. 18, 2021

Aug. 14 Epicenter

of earthquake

Aug. 16 Storm path of Grace

A magnitude-7.2 earthquake struck Haiti Saturday morning, killing more than 1,900 and leaving thousands injured and displaced from their homes. As people in the affected regions in the country’s southwest worked to recover with scarce res ources , a severe storm — Grace, then a tropical depression — drenched Haiti in heavy rain on Monday, bringing with it flash floods and the threat of mudslides , which could further delay recovery.

Area affected by earthquake

and storm in Haiti

Lower population

Damage reported

Petit-Trou-de-

Anse-à-Veau

Aug. 16, 8 p.m.

Storm batters Haiti

Aug. 17, 2 a.m.

Path of Tropical

Storm Grace

Aug. 16, 2 p.m.

Very strong shaking

Strong shaking

Moderate shaking

Light shaking

Path of Grace,

now a tropical storm

Although some light shaking from the earthquake could be felt as far as Haiti’s capital, Port-au-Prince, 80 miles from the epicenter, major damage was concentrated in the country’s Nippes, Sud, and Grand’Anse departments. When the shaking subsided, vast swaths of Haiti had ever so slightly moved. The map below shows displaced areas in Haiti, evidence of where the earth shifted after the earthquake.

Petit-Trou-

Epicenter of

magnitude-7.2

How much the ground

sank or rose

1 foot or more

A number of homes and school buildings were damaged in Les Cayes, a seaport community about 20 miles from the earthquake’s epicenter. Local hospitals were quickly overwhelmed , and a very limited number of doctors and surgeons worked through the night to triage victims. Temporary operating rooms near the main airport in Les Cayes were erected, as people tried to evacuate their loved ones to Port-au-Prince for emergency care.

Even before the quake, living conditions had been unstable for many Haitians as the pandemic added to severe poverty, gang violence and political trauma — the still-unsolved July 7 assassination of President Jovenel Moïse .

The earthquake also destroyed several churches that have served as sources of aid and stability to surrounding communities, especially to those that receive little support from the government.

Among the collapsed buildings in Les Cayes was Hôtel Le Manguier, where rescue teams continued to dig through the rubble and remove debris in the days after the earthquake hit.

Hôtel Le Manguier in Les Cayes

Jan. 24, 2020

Aug. 15, 2021

People in Les Cayes who lost their homes spent Monday night sheltering under plastic sheets in makeshift camps or fleeing flooded refugee camps as the storm passed through.

Jérémie, the capital city of the Grand’Anse department in Haiti, also suffered severe damage. Just five years ago, Jérémie was hit by Hurricane Matthew , which destroyed a wave of development that had brought hotels, cell phone service and new roads to the previously isolated region. Saturday’s earthquake caused destruction that overwhelmed the city’s main hospital and triggered a landslide that cut off access to the road leading to the city.

Like in Les Cayes, several churches in Jérémie were damaged, including the St. Louis King of France Cathedral, a landmark place of worship in the area that had also been damaged by Hurricane Matthew.

St. Louis King of France Cathedral in Jérémie

Aug. 14, 2020

Petit-Trou-De-Nippes

In Petit-Trou-De-Nippes, just five miles from the earthquake’s epicenter, phone lines were down in the area with no news immediately available. Landslides in nearby cities were recorded, according to the National Human Rights Defense Network, leaving parts of the Nippes department accessible only by motorcycle or sea.

Because of an editing error, an earlier version of this article misspelled the given name of the Haitian president who was assassinated last month. He was Jovenel Moïse, not Juvenel.

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Why Earthquakes In Haiti Are So Catastrophic

Jaclyn Diaz

Locals recover their belongings Sunday from their homes destroyed in the earthquake in Camp-Perrin in Les Cayes, Haiti. Joseph Odelyn/AP hide caption

Locals recover their belongings Sunday from their homes destroyed in the earthquake in Camp-Perrin in Les Cayes, Haiti.

It happened again.

Over the weekend, Haiti was hit by a magnitude 7.2 earthquake that crumbled homes and buildings and killed more than 1,200 people.

Rescuers are still working to find survivors amid the rubble. The death count is expected to rise.

More than a decade ago, a similar quake left an estimated 220,000 dead, more than 1 million people displaced and roughly 300,000 injured.

These two events are part of Haiti's history of major destructive earthquakes, records of which go back centuries.

Researchers say the country's unique geology make it seismically active — and prone to devastating earthquakes. A combination of factors, however, leaves the country especially susceptible to damage from these events.

Why is Haiti so susceptible to earthquakes?

Haiti sits on a fault line between huge tectonic plates, big pieces of the Earth's crust that slide past each other over time. These two plates are the North American plate and the Caribbean plate.

There are two major faults along Hispaniola, the island shared by Haiti and the Dominican Republic.

A map of the 2010 earthquake in Haiti shows dotted orange lines indicating fault lines. The nation sits on a fault line between huge tectonic plates of the Earth's crust — the North American plate and the Caribbean plate. Alyson Hurt/NPR hide caption

The southern one is known as the Enriquillo-Plantain Garden fault system.

It's this fault that the U.S. Geological Survey says caused Saturday's quake and the same one that caused the January 2010 earthquake.

The USGS believes the Enriquillo-Plantain Garden fault zone can be blamed on other major earthquakes from 1751 to 1860. The agency said none of these quakes has been officially confirmed in the field as associated with this fault, however.

Haiti Quake: Ruin And Recovery

The anatomy of a caribbean earthquake, a history of catastrophic earthquakes in haiti.

One of the earliest major recorded earthquakes in Haiti occurred in the 1700s, according to the USGS. Others followed, with researchers cataloging events that left hundreds dead and destroyed homes and businesses.

• Nov. 21, 1751: A major earthquake destroys Port-au-Prince and causes major destruction in nearby towns. Witness accounts of the event from the National Centers for Environmental Information recount the devastation . "Houses and factories were thrown down at St.-Marc, Lkogbne, and Plaine du Cul-de-sac. Crevices formed and abundant springs of nauseous water broke forth," researchers who witnessed the event described it. "Great landslips occurred and the beds of the rivers changed direction."
• June 3, 1770: An earthquake hits Port-au-Prince again. Researchers described the event as "one of the strongest shocks recorded on the Island of Haiti." An estimated 200 people in the nation's capital died as a result of the earthquake.
• April 8, 1860: This earthquake occurred farther west of the 2010 earthquake, near Anse-à-Veau, and was accompanied by a tsunami. "At Anse-a-Veau, crevasses sliced across the streets and 124 houses were demolished; at Miragoane, the bridge sank; at Petit Goave, all the houses were abandoned ... ," researchers said of the event. "Ships in the harbor of Les Cayes felt the shock, as did ships at sea."

Before the 2010 earthquake, there hadn't been another major quake along the Enriquillo-Plantain Garden fault zone for about 200 years.

In January 2010, people work to free trapped victims from the rubble of a collapsed building after an earthquake in Haiti's capital of Port-au-Prince. Gerald Herbert/AP hide caption

In January 2010, people work to free trapped victims from the rubble of a collapsed building after an earthquake in Haiti's capital of Port-au-Prince.

Building to withstand hurricanes, not earthquakes

The USGS says it recorded 22 magnitude 7 or larger earthquakes in 2010, the same year as the devastating earthquake in Haiti. However, despite an active year, almost all the fatalities were produced by the major temblor that hit on Jan. 12 of that year, the USGS said.

It struck around the densely populated capital of Port-au-Prince, contributing to the high death toll.

But the way structures are built in Haiti is also believed to have contributed to the loss of life and property.

Due to the 1751 and 1770 earthquakes and minor quakes that occurred between them, local authorities started requiring building with wood and forbade building with masonry, according to the USGS.

A woman tries to recover her belongings Sunday amid the rubble of her home destroyed by the quake in Camp-Perrin in Les Cayes. Joseph Odelyn/AP hide caption

A woman tries to recover her belongings Sunday amid the rubble of her home destroyed by the quake in Camp-Perrin in Les Cayes.

In the years since, Haitians have focused on building their homes to withstand the bigger threat in the neighborhood — hurricanes.

Structures made of concrete and cinder block hold up well during storms but are more vulnerable during earthquakes, according to The Associated Press .

More earthquakes may be ahead

In 2012, researchers wrote that the 2010 earthquake "may mark the beginning of a new cycle of large earthquakes on the Enriquillo fault system after 240 years of seismic quiescence."

"The entire Enriquillo fault system appears to be seismically active; Haiti and the Dominican Republic should prepare for future devastating earthquakes," researchers said.

It's still too early to determine the long-term impact of Saturday's earthquake. What is certain is the unique pressures facing Haitians in the days ahead.

The country still has not fully recovered from the 2010 earthquake and Hurricane Matthew in 2016.

Latin America

Ariel henry will become haiti's prime minister, ending a power struggle.

Haiti was already suffering from political instability following last month's assassination of President Jovenel Moïse. Moïse's death has since left a power vacuum that's been filled by interim Prime Minister Ariel Henry, a 71-year-old neurosurgeon and public official.

The nation is also bracing for another threat as Tropical Depression Grace threatens to bring heavy rains on Monday.

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A wake-up jolt? Assam’s 6.4 quake exposes its vulnerabilities

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• A 6.4 magnitude earthquake, measured on the Richter scale, rocked Assam in the early hours of April 28 this year. Two people died of shock and there was a lot of damage to property. There were at least 20 aftershocks.
• Soil liquefaction, when water seeps from the ground, was seen in places near the epicentre, near Dhekiajuli in the Sonitpur district.
• Scientists point that anthropogenic factors could contribute to earthquake triggers, although of smaller magnitude.
• More stringent monitoring of construction activities to ensure that the seismic code of safety is followed and awareness among people, are ways to mitigate the rising vulnerability of Assam as it lies in the highest seismic hazard zone.

When a strong, 6.4 magnitude earthquake shook Assam on April 28 this year, there was panic and mayhem. The earth cracked near the epicentre in the Sonitpur district, and so did walls and ceilings of people’s houses scores of miles in the radius; buildings swayed “like betel nut trees in the wind”, a hill broke down, and water seeped out of paddy fields. Already under the siege of the second wave of the COVID-19 pandemic, the earthquake — and the multiple aftershocks through the day — unleashed fear. Two people died of shock and there were several reports of considerable damage to houses and buildings. It also exposed, once again, the vulnerability of Assam to seismic activity and how anthropogenic activities could be further contributing to it.

Assam, and the entire northeast India, is categorised under seismic zone 5 , which means it’s extremely prone to high-intensity earthquakes. On April 28, the 6.4 magnitude earthquake measured on the Richter scale, was followed by 20 aftershocks of different magnitudes through the day, according to Gyanendra Dev Tripathi, CEO of Assam State Disaster Management Authority (ASDMA). Six aftershocks, of magnitude 3.2 to 4.7, occurred within hours of the main tremor. The National Centre for Seismology (NCS) has in fact continued to record seismic activity of magnitude 2.6-2.7 in the region on the eighth day of the main tremor.

The main tremor, said the NCS, occurred near the Kopili Fault, close to the Himalayan Frontal Thrust (HFT) which is a seismically very active area “associated with collisional tectonics where Indian plane sub-ducts beneath the Eurasian Plate”. A fault , according to the United States Geological Survey (USGS) “is a fracture or zone of fractures between two blocks of rocks. Faults allow the blocks to move relative to each other.” The Kopili fault is a 300 km northwest-southeast trending fault from the Bhutan Himalaya to the Burmese arc.

Earthquakes and Assam’s vulnerability

Earthquakes are not uncommon in Assam, with the NCS saying that the region has seen several moderate to high-intensity earthquakes. One of the worst among them was the great Assam-Tibet earthquake in 1950 which measured 8.6 magnitude on the Richter scale. Approximately 4,800 people were killed as a result, and there were several landslides that blocked the tributaries of the Brahmaputra and changed the topography of the region. The 1869 Cachar earthquake, measuring 7.4 magnitude, was another major seismic activity to hit the region.

Experts have said that recent seismicity discovered along the Kopili fault had led to speculations that it is one of the most seismically active faults of the region. A large portion of the Kopili fault region, said scientist Nilutpal Bora, and its neighbouring areas are characterised by alluvial soil that has a higher potential of trapping seismic waves and therefore making it one of the most earthquake-prone zones in northeast India.

“Assam, being located in the highest seismic zone, is perpetually challenged by the possibility of occurrence of earthquakes as an expression of release of accumulated tectonic stress,” Chandan Mahanta, professor in the department of civil engineering, Indian Institute of Technology (IIT) Guwahati, told Mongabay-India. Continuous tectonic stress keeps building up along the fault lines, he said, and the 6.4 magnitude tremor was a release of such accumulated stress.

One thing leads to the other

High-intensity tremors aside, the region is vulnerable to seismic activity of different magnitude and intensity. This, said Mahanta, could be a contributing factor to erosion, since “seismic activity can disturb earth material properties, like strength and cohesion, and slope instability adds to this”.

Images of a portion of a hill breaking and falling into a river in the Udalguri district following the 6.4 magnitude tremor showcased to the rest of the world the intensity of the quake. The 1950 quake had led to many landslides and Mahanta said that apart from the major quakes mentioned, “many landslides are seismologically induced”. This means that seismic activity has a role to play in adding sediment load to the Brahmaputra river. “Landslides in upper Brahmaputra are known to add high sediment load to the river,” Mahanta said.

This is significant because a high sediment load on the Brahmaputra is known to cause recurrent floods since the river bed rises and the width of the river increases. Dredging of the river, the Assam government has long said, is a solution to this problem, allocating huge amounts of funds to this end. In 2017, union minister of transport, Nitin Gadkari, had announced Rs 250 crores for dredging the Brahmaputra. Experts, however, opine that dredging the entire river is neither a feasible nor a permanent solution since the silt makes its way back after being removed.

When water guzzled out of the earth

This April’s tremor also led to a seemingly ‘strange’ event: of water springing out of paddy fields, close to the epicentre, near Dhekiajuli, in Assam. A video of this was shared on social media by the present state chief minister Himanta Biswa Sarma. Scientists call this phenomenon, soil liquefaction. By definition, it means when saturated or partially saturated soil substantially loses strength and stiffness in response to applied stress, like the shake of an earthquake.

And in this case, Vineet Gahalaut, chief scientist, CSIR-National Geophysical Research Institute, said it was nothing out of the ordinary particularly because “it is common in places with shallow water table”.

“In 2017, the Manu earthquake in Tripura caused soil liquefaction till Bangladesh. And its magnitude was 5.7 on the Richter scale,” Gahalaut said.

Anthropogenic factors at play?

What should be considered more importantly, is the possibility of anthropogenic factors impacting seismic activity. “Whether anthropogenic factors can cause an earthquake of this magnitude (6.4) is difficult to establish. But there have been few cases in the US, where seismic monitoring is good, where it has been seen that anthropogenic factors may have caused small magnitude earthquake and seismic activity,” Gahalaut told Mongabay-India.

As an example, he said, excessive mining, geothermal pumps, construction of dams, and injecting water under high pressure in oil reserves to crack the area in order to release fluid and oil may “trigger” seismic activity. A research paper , ‘ Influence of anthropogenic groundwater unloading in Indo-Gangetic plains on the April 25, 2015 Mw 7.8 Nepal Earthquake ’—of which Gahalaut is a co-author—talks along similar lines.  “Tectonic process and anthropogenic factors are two very different things, but like the last straw on the camel’s back, when the pressure is already high and in a critical position, human activity can trigger an earthquake,” Gahalaut said.

Mitigating vulnerabilities

For northeast India and for Assam which is in the highest probability zone in terms of earthquake hazard, the vulnerability quotient is high and increasing. “Construction on hills, mushrooming high-rises increase the vulnerability factor,” Tripathi of ASDMA told Mongabay-India, “The way to mitigate this vulnerability is to ensure all construction follow the seismic code of safety and making people aware of safety measures,” he said.

Whether every building in Assam and in particular Guwahati — “especially the new ones,” said an expert — is following the code, however, is questionable.

“There is no strong supervisory mechanism or regulatory policy to ensure that this code is followed in all construction,” Tripathi said.

Mahanta suggests that “high-resolution, micro zonation-based planning and building design following the correct seismic code” is the key to building safety which is crucial in a place like Assam. A 2007 seismic microzonation atlas of Guwahati region is a case in point.

Interestingly, the tremor also brought into limelight the good-old, single-storeyed ‘Assam-type’ houses which were built with indigenous material and were more capable of resisting earthquakes. Fast disappearing from urban areas, the jolt has revved up nostalgia on social media and has spurred conversations around the restoration of such ancestral houses.

Banner image: Seismic activity has a role to play in adding sediment load to the Brahmaputra river. Photo by VINOYBLOG/Wikimedia Commons.

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Case Study: Predicting the Next Big Earthquake

Recent earthquake activity.

USGS Recent Worldwide Earthquake Activity To explore individual earthquakes in more depth, click on the UTC Date-Time field. Show me how Hide Details for accessing USGS Recent Worldwide Earthquake Activity Scroll the list to look over earthquakes that have occurred in the last seven days. To explore individual earthquakes in more depth, follow the COMMENTS links. Scroll to the bottom of the list to view recent Earthquakes plotted on a world map. What is the magnitude of the most recent recorded earthquake? How many earthquakes were recorded for the last seven days? Of those earthquakes, how many were of a magnitude 7.0 or greater? IRIS Seismic Monitor Click on the map to zoom to specific regions. Click on individual earthquakes to see lists of others nearby. Show me how Hide Details for accessing the IRIS Seismic Monitor Click on the map to zoom to specific regions. Click on individual earthquakes to see lists of others nearby. Where are earthquakes concentrated?

Where does Earth Quake?

Predicting the Next Big One!

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• 03 April 2024

Taiwan hit by biggest earthquake in 25 years: why scientists weren’t surprised

• Gemma Conroy

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A building in Hualien, Taiwan, leans dangerously after a magnitude-7.4 earthquake on 3 April 2024. Credit: VCG via Getty

Scientists warn that more shocks are likely after Taiwan was rocked by the most powerful earthquake to hit the island in 25 years. The quake killed several people, flattened buildings and triggered landslides. Geologists say that the epicentre was in a complex network of offshore faults, which makes aftershocks or even another quake a possibility.

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Nepal Earthquake Case Studies

About the Project

On April 25, 2015, Nepal and its people experienced a 7.8 magnitude earthquake. On May 12, another major earthquake of 7.2 magnitude hit the country. In practice, his means that millions of Nepalis have lived and died under the weight of falling buildings, landslides, floods, hunger, and homelessness brought about by massive seismic shifts across the Himalayan belt. Most will refer to this as an earthquake, singular. But this is no singular disaster. The country has experienced more than 300 seismic events since April 25, 2015, and nearly 9000 people died as a direct result of the two most major earthquakes.

For most of Nepal’s approximately 30 million people, living uncertainty is old hat. Consider the legacies of civil war (1996-2006) followed by a decade of political instability and current struggles to write a viable constitution. But the spring of 2015 has cracked open new forms of vulnerability for most Nepalis. These quakes have caused enormous destruction to the nation’s rich cultural heritage, in the Kathmandu Valley and beyond. The countryside has experienced vast devastation. More than half a million homes have been destroyed or are precariously habitable. This equates to about 2.5 million internally displaced. More than 3,500 schools have been destroyed and nearly as many health posts. There has been widespread damage to highways and road networks; glacial lakes are in danger of bursting; landslides are a constant threat, and have continued to wipe out settlements; many hydroelectric dams have been damaged; water borne illness and other public health challenges loom as monsoon has arrived. Even so, Nepalis are showing incredible resilience, creativity, and deep commitments to helping each other through this suffering.

This project – in the context of ANTH 55: Anthropology of Global Health – explores the human impacts of these disasters by asking students to engage in collective research and writing of case studies focused on specific areas of inquiry related to the earthquake.

The assumption of this project is not that students will become “experts” either on Nepal or on the health effects of earthquakes, but that they will amass sufficient knowledge about their area of inquiry so that they can contribute to an effort to expand knowledge and understanding of this event to others, and expand in the process their own conceptualization of what “global health” is, where and how it occurs, and how it links to many other aspects of human life.

Article  

• Volume 24, issue 9
• NHESS, 24, 3129–3154, 2024
• Peer review
• Related articles

Forearc crustal faults as tsunami sources in the upper plate of the Lesser Antilles subduction zone: the case study of the Morne Piton fault system

Melody philippon, jean-frédéric lebrun, isabelle thinon, océane foix, stéphane mazzotti, marc-andré gutscher, leny montheil, jean-jacques cornée.

In this study, alternatively to the megathrust, we identify upper-plate normal faults orthogonal to the trench as a possible tsunami source along the Lesser Antilles subduction zone. The Morne Piton fault system is such a trench-perpendicular upper crustal fault at the latitude of Guadeloupe. By means of seismic reflection, high-resolution bathymetry, remotely operated vehicle (ROV) imaging and dating, we reassess the slip rate of the Morne Piton fault since 7 Ma, i.e., its inception, and quantify an average rate of 0.25 mm yr −1 since ca. 1.2 Ma. This result divides by two previous estimations, increases the earthquake time recurrence and lowers the associated hazard. The ROV dive revealed a metric scarp with striae at the toe of the Morne Piton fault system, suggesting a recent fault rupture. We estimate a fault rupture area of ∼  450–675 km 2 and then a magnitude range for a maximum seismic event around M w  6.5  ±  0.5, making this fault potentially tsunamigenic as the nearby Les Saintes fault responsible for a tsunami following the 2004 M w  6.3 earthquake. Consequently, we simulate a multi-segment tsunami model representative of a worst-case scenario if all the identified Morne Piton fault segments ruptured together. Our model provides clues for the potential impact of local tsunamis on the surrounding coastal area as well as for local bathymetric controls on tsunami propagation. We illustrate that (i) shallow-water plateaus act as secondary sources and are responsible for a wrapping of the tsunami waves around the island of Marie-Galante; (ii) canyons indenting the shallow-water plateau slope break focus and enhance the wave height in front of the most touristic and populated town of the island; and (iii) the resonance phenomenon is observed within the Les Saintes archipelago, showing that the waves' frequency content is able to perturb the sea level for many hours after the seismic rupture.

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Philippon, M., Roger, J., Lebrun, J.-F., Thinon, I., Foix, O., Mazzotti, S., Gutscher, M.-A., Montheil, L., and Cornée, J.-J.: Forearc crustal faults as tsunami sources in the upper plate of the Lesser Antilles subduction zone: the case study of the Morne Piton fault system, Nat. Hazards Earth Syst. Sci., 24, 3129–3154, https://doi.org/10.5194/nhess-24-3129-2024, 2024.

Regions in the vicinity of active subduction zones are prone to seismic and related hazards, including tsunamis, exposing their inhabitants to multiple threats. Megathrust earthquakes represent the greatest threat with the highest seismic moments and consequently huge tsunamigenic potential (Satake and Tanioka, 1999). Earthquakes triggered on crustal faults in the overriding plate represent an additional hazard that needs to be quantified (Bilek, 2010). In order to assess the hazards and mitigate the risks associated with these crustal faults, it is essential to estimate their slip rates.

On land, slip rates on active faults are determined from paleo-seismic trenches (McCalpin, 1996), high-resolution geophysical investigation (Wallace, 1981; Zhang et al., 2014), satellite imagery (Tronin, 2009), InSAR (Biggs and Wright, 2020), geodetic measurement (GNSS, Symithe et al., 2013) and seismicity, which account for the present-day strain accumulation of the crust. Offshore, slip rate estimates are provided by means of underwater geodesy (i.e., acoustic geodesy, Kido et al., 2006; Petersen et al., 2019; Fujita et al., 2006) or fiber optic monitoring (Hirata et al., 2002; Gutscher et al., 2019). The recurrence time of events may be estimated by the study of turbidite deposits cores (e.g., Cascades, Goldfinger et al., 2012; Taiwan, Lehu et al., 2016; Antilles, Seibert et al., 2020; New Zealand, Lewis, 1980), high-resolution marine seismic and multibeam echo-sounder data (e.g., Escartín et al., 2016, 2018), and submarine survey dives (e.g., Geli et al., 2011). However, constraining hazard models in areas undergoing slow strain rates remains challenging as the earthquakes' recurrence time overcomes the historical period. Indeed, geodetic measurements require decade-long time series as the resolution of the method is not accurate enough, and erosion or high sedimentation rates may have erased or covered, respectively, the active fault scarps, making it difficult to identify active fault segments. Therefore, datasets based on the last 10 to 100 years of record along tectonic systems undergoing slow strain rates may not be representative of the bulk strain and may be at the origin of biased estimations of the slip rate along these faults.

The Lesser Antilles (eastern Caribbean) records show slow deformation rates as the North and South American tectonic plates slowly subduct under the Caribbean plate (20 mm yr −1 , Fig. 1). Extensional tectonics and normal faulting affect the forearc (Feuillet et al., 2002; De Min et al., 2015; Boucard et al., 2021), but available historical data do not report tsunami events related to forearc fault rupture. However, the Les Saintes M w  6.3 earthquake of December 2004 ruptured the Roseau normal fault (Feuillet et al., 2011; Bazin et al., 2010). The earthquake reached an intensity up to VIII in the Guadeloupe archipelago (Fig. 1), was felt by most of its ∼  400 000 inhabitants and was responsible for one casualty. This earthquake triggered a tsunami with up to 2 m high waves at the coast and a maximum measured run-up distance of 42 m in Les Saintes (Zahibo et al., 2005; Le Friant et al., 2008; Cordrie et al., 2020). Prior to this event, this fault was unmapped and therefore not identified as an active fault (Feuillet et al., 2002; Terrier et al., 2002). Forearc normal faults, similar to Les Saintes fault system, may pose a threat to the 4 million inhabitants of the Lesser Antilles that are living on volcanic arc islands facing the subduction trench to the east and literally sitting over the subduction interface.

Figure 1 (a)  Synthetic tectonic map of the Lesser Antilles forearc. Structures after Feuillet et al. (2002), Legendre et al. (2018) and Boucard et al. (2021). Thick red and green lines indicate the location of the wide-angle seismic lines from (b) Kopp et al. (2011) and (c) Padron et al. (2021), respectively. White star: location of tsunamigenic earthquakes. Thick white contour lines: slab depth isocontour from Bie et al. (2020).

The present study focuses on the Morne Piton fault system, perpendicular to the subduction trench, which is one of the most prominent onshore–offshore fault systems and cuts the Guadeloupe archipelago arc and forearc islands (Fig. 1). Regarding the seismic and tsunami hazards related to this fault system and the vulnerability of the coastal population and infrastructures of the archipelago, the objectives are to (1) estimate the fault slip rate; (2) determine the geometry of the fault segments; and (3) model the associated tsunami hazard, since such a joint approach has been lacking so far.

In this paper, the fault geometry is refined in order to provide an up-to-date map of the fault segments thanks to high-resolution (HR) bathymetric data. Then, we integrate its long-term slip rate over the last ca. 7 Myr, i.e., from fault initiation to the present day, by means of HR seismic reflection lines and available biostratigraphic and isotopic dates. Secondly, remotely operated vehicle (ROV) explorations of seafloor rupture allowed us to measure the height of the fault scarp and to determine the fault kinematics from striations observed along a recent coseismic scarp. Because the overall geometry of this fault system is comparable to the Les Saintes fault system in terms of length, seafloor scarp and dip, we postulate that a rupture along the Morne Piton fault may trigger a local tsunami close to the coasts of the Guadeloupe archipelago. Therefore, we study the seismogenic and tsunamigenic potential of the Morne Piton fault system, providing an overview of what could happen in terms of tsunami generation if all the segments of the Morne Piton fault ruptured simultaneously, i.e., a plausible worst-case scenario. This scenario allows us to identify and discuss the local bathymetric controls on the propagation of the resulting tsunami wave and the consequences (e.g., amplifications and interferences) in near-shore areas of the neighboring populated islands. We do not assess coastal inundation scenarios, as our scenario cannot be refined by observational rupture data accurate enough to realize such a specific hazard study. Finally, we conclude on the importance of forearc crustal faults as potential major tsunami sources in subduction zones.

Oceanic lithosphere of the North and South American plates is slowly subducting beneath the Caribbean plate at a convergence rate of ∼  20 mm yr −1 (Fig. 1, DeMets et al., 2000; Philippon and Corti, 2016). The convex trench geometry results in along-strike variations in obliquity, increasing northward from Guadeloupe. Along the arc, oblique subduction is accommodated by trench-parallel left-lateral strike-slip faults such as the Montserrat–Havers–Bouillante and Les Saintes corridor (located within the volcanic arc), the Bunce fault (located along the crustal buttress) and a series of trench-perpendicular grabens forming a sinistral horsetail (Feuillet et al., 2002, 2010; ten Brink et al., 2004; Boucard et al., 2021; Figs. 1, 2a).

Figure 2 The Marie-Galante basin (a)  structural pattern after Feuillet et al. (2002) and De Min et al. (2015) on the shaded-relief bathymetric map. Blue hexagons: tide gauges https://data.shom.fr/donnees/refmar/ (last access: October 2022). Red color scale: Guadeloupe population density per square kilometer after GEOFLA ( https://www.data.gouv.fr/fr/datasets/geofla-r/ , last access: October 2022). (b)  Seismostratigraphic scheme of the Marie-Galante basin modified after Cornée et al. (2023). (c)  Colored dots: crustal seismicity from the International Seismological Centre (2023) and USGS (2017) databases for earthquakes (EQ) of magnitude 3  >   M w   >  6.5, located from 0 to 30 km depth; the red line shows the WAS line (Kopp et al., 2011). (d)  Focal mechanism solutions are indicated by red-and-white beach balls after Gonzalez et al. (2017). The location of historical earthquakes is indicated by black stars (after Feuillet et al., 2011). AP, PdC, PAP and PT stand for Anse Piton, Pointe des Chateaux, Pointe-à-Pitre and Petite-Terre.

In the central Lesser Antilles, the Marie-Galante basin (Guadeloupe archipelago) is located at the southern end of the aforementioned regional horsetail system and is described as a conjugated normal fault system defining a trench-perpendicular graben (Fig. 2a; Feuillet et al., 2001, 2011). This graben affects sediment deposits comprising three regional mega-sequences: an Eocene–Early Miocene MG-MS1 sequence, a Middle Miocene–late Tortonian/early Messinian MG-MS2 sequence and a Messinian–present MG-MS3 sequence (Bouysse et Mascle, 1994; De Min et al., 2015; Cornée et al., 2023). It shapes the Marie-Galante basin (up to 1200 m water depth) and surrounding Grande-Terre and Marie-Galante islands (Fig. 1). The northern boundary of the Marie-Galante basin is the east-trending, south-dipping Gosier fault that runs primarily onshore along the southern coast of Grande-Terre (Garrabé and Andreieff, 1988; Fig. 2a). The southern boundary of the basin consists of the N100° E-trending, ∼  50 km long, north-dipping Morne Piton fault, which crosscuts the northern edge of Marie-Galante island (Bouysse et al., 1993) and extends offshore on both sides of the island (Feuillet et al., 2002, 2004).

The Morne Piton fault system consists of five main 5–15 km long segments trending N90° E  ±  30° separated by N140° E shorter right-lateral relays (Fig. 2). The fault scarp is exposed at Anse Piton, eastern coast of Marie-Galante, and shows dip-slip striations (Feuillet et al., 2002). Onshore Marie-Galante, the fault offsets the Pliocene to Middle Pleistocene platform by ∼  60 m. It also crosscuts a series of three uplifted late Middle to Late Pleistocene terraces along the eastern side of the island. Feuillet et al. (2004) calculated a 5 km dislocation depth and a 70 to 80° N fault dip to model the observed flexure of the footwall. Considering that the Marie-Galante plateau is a flat abandoned 330 ka marine terrace, these authors estimate the average slip rate of the Morne Piton at about 0.5±0.2  mm yr −1 since 330 ka. Regarding the uplifted terraces, they estimated a maximum earthquake moment magnitude ( M w ) ranging from 5.8 up to 6.5 with a recurrence time of 400–1000 to 1400–3300 years, respectively (250 km 2 of the estimated ruptured area). Moreover, it was later demonstrated that this plateau emerged between 1.77 and 1.07 Ma (magnetostratigraphic chron 1R2r: Cornée et al., 2012; Münch et al., 2014; De Min et al., 2015; Léticée et al., 2019; Cornée et al., 2021). Note that considering an older age for the plateau emergence would drastically lower the slip rate estimate and increase the recurrence time calculated by Feuillet et al. (2001).

Upper-plate seismicity in the Marie-Galante basin provided by the (i) CDSA seismic database (Antilles Seismological Data Center, Bengoubou-Valerius et al., 2008; Massin et al., 2021), (ii) IEB mixed database USGS and ISC ( https://www.isc.ac.uk , last access: September 2024) (Fig. 2b) and (iii) deployment of ocean-bottom seismometers (OBSs; Ruiz et al., 2013; Bie et al., 2020) shows a widely distributed pattern of moderate-magnitude earthquakes ( M w ≤5.3 ), with the exception of the 2004 seismic cluster in Les Saintes. Wide-angle seismic (WAS) profiles together with earthquakes data indicate a seismogenic crustal thickness limited to the first 15–20 km west of Marie-Galante, suggesting a brittle–ductile transition at this depth (Kopp et al., 2011; Ruiz et al., 2013; Gonzalez et al., 2017; Padron et al., 2021). Among the very few focal mechanisms available in the Marie-Galante basin (Gonzalez et al., 2017), the 25 February 2014 M w  3.8 earthquake occurred beneath the southern Grande-Terre platform and shows pure normal motion along sub-E–W-trending nodal planes (Gonzalez et al., 2017; event no. 9; hypocentral location accuracy of ca. 5 km; Fig. 2c). The location, depth and nodal plane characteristics (57° dip and N102° E) of the earthquake indicate that the event may correspond to a rupture along the Gosier fault system, which is the only major fault system in the vicinity of the hypocentral location able to trigger an earthquake of such magnitude. Feuillet (2000) provided more than 20 focal mechanisms for earthquakes showing a local magnitude ranging between 2  <   M l   <  3.7 and one M s =  5.6 earthquake, located in and around the Marie-Galante graben. All focal mechanisms show nearly pure normal motion along sub-E–W-trending nodal planes, consistent with kinematics indicators observed along the Gosier and Morne Piton faults. This tectonic pattern is confirmed by GNSS velocities, which indicate that a small trench-parallel extension is accommodated in the upper-plate forearc (van Rijsingen et al., 2021).

Two historical earthquakes are reported along these two fault systems: (i) the 16 May 1851 earthquake with a maximum intensity of VII recorded in the southeastern part of Basse-Terre is attributed to the Morne Piton fault, with an estimated moment magnitude M w =  6.0 (Feuillet et al., 2011), and (ii) the 29 April 1897 earthquake with a maximum intensity of VIII recorded in the Pointe-à-Pitre area is attributed either to the Gosier fault system, with an estimated moment magnitude M w =  5.5, or to the Montserrat fault zone, with an estimated moment magnitude M w =  6.5 (Bernard and Lambert, 1988; Feuillet et al., 2011). Overall, at the latitude of Guadeloupe, regional earthquake data suggest that normal fault systems are active and have an ability to generate earthquakes of moment magnitudes of M w  6 and above. This magnitude range is potentially able to trigger tsunamis according to tsunami catalogues (as explained, for example, in Roger et al., 2019).

Southwest of the Marie-Galante basin, the 2004 M w  6.3 earthquake (Bazin et al., 2010; Feuillet et al., 2011) showed that upper-plate crustal faults can generate strong earthquakes and tsunamis. The main shock occurred along the NNW–SSE-trending, ca. 40 km long arc-parallel Les Saintes fault System (Feuillet et al., 2011; Leclerc et al., 2016). The recurrence interval of such a rupture is estimated to be a few hundred years or more (Escartín et al., 2016, 2018; Feuillet et al., 2011; Le Friant et al., 2008). Focal mechanisms of the main shock and five aftershocks provided an overall pure normal motion along NNW–SSE nodal planes (Fig. 2d). Source models from Salichon et al. (2009), Bazin et al. (2010) and Feuillet et al. (2011), well constrained by the long duration of the aftershock sequence, proposed a main source localized along the N135° E-trending, 50° E-dipping Roseau fault (westernmost fault of the Les Saintes fault system), with a 30 km long and 21 km downdip width fault plane. The aftershock seismicity reactivated several nearby conjugate faults, with a maximum seismic depth at ca. 15 km. The main rupture occurred at two asperities located 8 km below the surface, with a maximum slip of 1.8 m, and propagated to the surface, triggering a coseismic offset of the seafloor of 0.3–0.6 m along a ca. 10 km long segment. Escartín et al. (2016) investigated the fault scarp by means of HR bathymetry, highlighting a 3 km long, up to 0.9 m high scarp, but concluded that part of the observed slip may be post-seismic. The Les Saintes earthquake generated up to 2 m high tsunami waves at the coast and a maximum horizontal run-up of 42 m in some bays of Les Saintes (Zahibo et al., 2005; Le Friant et al., 2008; Cordrie et al., 2020). However, tsunami models using fault parameters based on seismological data resulted in an underestimation of the tsunami wave amplitude and run-up (Le Friant et al., 2008). Cordrie et al. (2020) consider that their best-fit models require greater slip on the fault plane and a greater magnitude for the earthquake than those given by the seismological data in order to accurately reproduce the observed tsunami, suggesting that the observed scarp is the surface expression of coseismic slip (source parameters: M w =  6.4–6.5; fault plane, 15×15  km; strike, N325° E; dip, 55° E; rake, ca. 90°; slip  =  2.5–3.5 m).

Over the last ∼  500 years of historical written archives in the Lesser Antilles, a few dozen confirmed tsunamis from different origins (local, regional or far-field sources including earthquakes, landslides, volcanic eruptions or combinations of them) have been reported. Starting with the 16 April 1690 M s   ∼  8.0 Barbados earthquake (which presumably triggered the first reported tsunami in the Lesser Antilles), it includes the widely studied 1 November 1755 Lisbon transoceanic tsunami (e.g., Gutscher et al., 2006; Accary and Roger, 2010; Roger et al., 2010, 2011; Martínez-Loriente et al., 2021) and the 18 November 1867 Virgin Islands tsunami (e.g., Zahibo et al., 2003, 2005; Barkan and ten Brink, 2010). Landslide sources or pyroclastic flows are also known for their tsunamigenic potential. In recent years, more and more studies have been carried out to assess the hazards associated with these “silent” tsunamis (e.g., Roger et al., 2024). In the Caribbean region, a few tsunamis triggered by landslides or pyroclastic flows have been reported in catalogues of events (e.g., O'loughlin and Lander, 2003; Accary and Roger, 2010), bathymetric surveys helped to identified large submarine landslide scars and deposits (e.g., Deplus et al., 2001; Le Friant et al., 2009, 2019), and a few studies have highlighted the capacity of these landslides to trigger large tsunamis (e.g., Smith and Shepherd, 1996; Teeuw et al., 2009; Leslie and Mann, 2016).

On the basis of an extensive literature review, including cross-checking of information, we conclude that only four tsunamis reported in Guadeloupe are likely of upper-crust seismic origin (Mallet, 1853, 1854, 1855; Lander, 1997; Zahibo and Pelinovsky, 2001; Lander et al., 2003; O'Loughlin and Lander, 2003; Zahibo et al., 2003; Accary and Roger, 2010; Nikolkina et al., 2010; Roger et al., 2013; online databases National Geophysical Data Center/World Data Service (NGDC/WDS), NOAA 2024, and Tsunami Laboratory/Institute of Computational Mathematics and Mathematical Geophysics (TL/ICMMG), 2023). These tsunamis have been observed or recorded following earthquakes occurring on regional faults (indicated magnitude and epicenter coordinates are from the USGS online earthquake catalogue: https://www.usgs.gov/programs/earthquake-hazards , last access: October 2022): the M w   ∼  8.0–8.5 earthquake on 8 February 1843 (NE of Guadeloupe, 16.73° N, 61.17° W) and the M w  7.2 earthquake on 25 December 1969 (SE of Guadeloupe, 15.648° N, 59.694° W), which are arguably attributed either to a rupture along the megathrust or to upper-plate faulting; the M w  6.5 earthquake on 16 March 1985 (along the Montserrat–Havers–Bouillante fault system between Montserrat and Nevis, north of Basse-Terre, 17.013° N, 62.448° W); and the M w  6.3 earthquake on 21 November 2004 (along the Les Saintes fault system, south of Basse-Terre, 15.679° N, 61.706° W; Fig. 1). The largest earthquakes and tsunamis produced at subduction zones are expected to originate from rupture at the plate interface megathrust. However, historical records in the Lesser Antilles reveal that neither the 1843 M w  7.5–8.5 nor the 1839 M w  7.5–8.5 largest known earthquake, although destructive, has been followed by large tsunamis. However, Roger et al. (2013) showed that the simulation of a M w  8.5 1843-like megathrust earthquake would have produced wave amplitudes of 5 m and more along the exposed coasts of Guadeloupe, which was not reported in coeval documents. Feuillet et al. (2011) explain that these two major earthquakes had a great rupture depth along the megathrust, consequently leading to slight seafloor deformation. However, numerical simulations of worst-case scenarios for these two ruptures along the megathrust evidence the possibilities of tsunami amplitudes up to 10 m and above in some embayment (Roger et al., 2013; Colon-Useche et al., 2023). As the magnitude of crustal earthquakes is constrained by the fault length, events occurring along such a crustal fault show a much smaller magnitude than megathrust earthquakes, which consequently may form smaller seafloor offsets. Thus, most crustal earthquakes that are able to trigger a tsunami do not produce significant sea surface deformation (only a few centimeters amplitude in most cases) compared to subduction interface earthquakes. Associated tsunamis are typically only visible on pressure gauge records (coastal gauges or DART systems) after processing the data (e.g., de-tiding and high-frequency filtering).

5.1  Seismic lines

We present eight multichannel seismic (MCS) lines acquired during five oceanographic campaigns (location in Fig. 3a; uninterpreted profiles are provided as Supplement Figs. S1 and S2). These include high-resolution sparker source seismic data from KaShallow 1 (Lebrun et al., 2008) and GEOBERYX03 oceanographic campaigns (Thinon and Bitri, 2003; Thinon et al., 2004, 2010), mid-resolution GI airgun array seismic data from KaShallow 2 (Lebrun et al., 2008) and Aguadomar (Deplus et al., 1998) cruises, and deep-penetrating MCS data from the Sismantilles 1 seismic experiment (Hirn, 2001; Table 1).

Figure 3 (a)  High-resolution (25 m grid spacing) bathymetric map (UMO16) of the Marie-Galante basin, offshore Guadeloupe, and the location of the seismic profiles shown in Figs. 4 and 5, as well as the location of the dredge samples used for the seismic unit age calibration (Münch et al., 2013). (b)  Structural interpretation of the E–W-trending Morne Piton fault system. (c)  A proxy for cumulative strain given by the graphic displaying the fault surface displacement, taken as the difference between the top and the toe of the fault scarp versus L (fault length) along the whole system.

Table 1 Main acquisition parameters of the seismic data shown in this study (Figs. 4 and 5); CDP stands for common depth point.

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Sismantilles 1 seismic data were processed using CGG Veritas Geovecteur ® software on board the R/V  Nadir (Hirn et al., 2001). Processing includes band pass filtering, internal and external mute, one-step velocity analysis, normal-moveout (NMO) correction, stack, predictive deconvolution, and post-stack constant water-velocity time migration. KaShallow 1 and 2, Aguadomar, and GEOBERYX03 were processed with Seismic Unix software (Cohen and Stockwell, Center for Wave Phenomena, Colorado School of Mines). The seismic processing includes band pass filtering, sea waves and spherical divergence corrections, constant velocity or simple velocity gradient NMO correction and stack, and constant water-velocity time migration. The reflection seismic lines are in millisecond two-way travel time (mstwt). The velocities of the wide-angle seismic (WAS) refraction profiles are in second two-way travel time (stwt).

5.2  Bathymetry

High-resolution bathymetric data were acquired during the KaShallow 2 oceanographic campaign (Lebrun, 2009) using a Simrad EM300 multibeam echo sounder. We merged these data with the Aguadomar (Deplus, 1998) and Sismantilles 2 (Laigle et al., 2007) cruise Simrad EM12 dual multibeam echo-sounder data available for the Marie-Galante basin. Vertical accuracy for these echo sounders is plurimetric for the typical water depth found in the Marie-Galante basin ( <  2000 m below mean sea level, noted b.s.l. hereafter). Near-shore (0–200 m b.s.l.) and onshore, very high resolution bathymetric and topographic data come from the Litto3D database – https://www.geoportail.gouv.fr/donnees/litto3d (last access: 2 October 2022) – which includes airborne lidar survey and KaShallow 3 multibeam data acquired with a RESON SeaBat 8101 multibeam echo sounder. The vertical accuracy for this second dataset is better than 1 m. We used the Caraibes software (Ifremer) to process the data and to produce a 25 m grid spacing digital elevation model of the Marie-Galante basin and surrounding islands. Maps are produced using the open-access QGIS software ( https://www.qgis.org , last access: August 2024).

5.3  Depth and time calibration of main geological boundaries

In order to measure offsets of unconformities on time-migrated seismic lines, we need to constrain the seismic velocities within the sediments. We used velocities from the WAS profile (Kopp et al., 2011) in the south of Marie-Galante that trends parallel to the MCS line Agua116 (Cornée et al., 2023). The WAS velocities in the ca. 0.4 stwt (second two-way time) thick upper unit (MG-MS3, Cornée et al., 2023) range between 2 and 2.5 km s −1 . The 3.25 km s −1 isochrones mimic the base of unit MG-MS2, and the 4.5 km s −1 isochrones follow the acoustic basement below MG-MS1. Moreover, KaShallow 2 cruise MCS data (Table 1) acquired with a 600 m long streamer allow us to determine the normal-moveout velocities down to a depth of ca. 0.75 stwt in well-layered units such as shown by the seismic lines (Fig. 3). Once converted into interval velocities using the Hewitt Dix formula, we determine velocities in the upper unit from 1500 to 2750 m s −1 (Dix, 1955). Therefore, we use 1500 m s −1 in the water and 2000 and 2500 m s −1 in the sediments to estimate (and bound) the depth of unconformities observed on time-migrated seismic lines (Table 2).

Table 2 Measured offset of seismic reflectors across the Morne Piton fault system and calculated total vertical strain rates. See text for the age estimate. Seismic reflector depth on each side of the fault system is measured in time (stwt, second two-way time) and converted into depth using water velocity (1500 m s −1 ) and two end-member velocities for the sediment (see text for explanation), providing a minimum and a maximum offset value. The minimum strain rate is obtained from the ratio between the minimum offset and the maximum age bound of the reflector and vice versa.

Offshore, several first-order unconformities and sedimentary units were accurately dated using biostratigraphy analysis or radiochronology (Bouysse and Mascle, 1994; KaShallow research program results, Münch et al., 2013; De Min et al., 2015; Cornée et al., 2023). The deepest dated unconformity, MG-SB2, which corresponds to the top of the MG-MS1 sequence, occurs on seismic lines east of Marie-Galante (thick orange line in Fig. 5, lines AGUA97, K09-09, K09-45 and Sis7C). Along the seismic line Agua97, the F8 fault scarp was sampled at 514 m b.s.l. just beneath the unconformity (KaShallow cruise ROV dive, Fig. 6). The samples BMG2 and BMG4 yielded a late Burdigalian/earliest Langhian age (Cornée et al., 2023). Thus, we propose 16±1  Ma for the age of MG-SB2. Above, another regional unconformity, MG-SB3 (Cornée et al., 2023), is identified east of Marie-Galante. It corresponds to the top of the MG-MS2 sequence (thick purple line in Fig. 5, lines Agua97, K09-09-08, K09-45-44 and Sis7C). The age for this surface is bracketed between the late Messinian Grande-Terre (GT) carbonate platform (zones N18; 5.8–5.33 Ma; Cornée et al., 2023) and the sedimentary unit dated late Tortonian, 8.57±0.43  Ma (Ar–Ar, Münch et al., 2014). We thus consider 7±1.5  Ma for the age of MG-SB3. West of Marie-Galante, the angular unconformity on line K09-90 northwest of Marie-Galante may corresponds to MG-SB3 (Fig. 4). However, this reflector is too deep to be followed across the whole fault system. Within the uppermost sequence, MG-MS3, a remarkable unit boundary corresponding to a second-order unconformity can be easily correlated throughout the basin and onshore (thick red line in Fig. 4). This unit boundary is middle–late Piacenzian offshore, and it correlates with the 3–2.9 Ma tectonically induced erosional unconformity SB1 onshore (see above; Cornée et al., 2023). Along the seismic line Ber03-30-31, the fault scarp immediately north of F3 and F4 was sampled at 283 m b.s.l. (KaShallow cruise ROV dive, Fig. 4). Samples BC1 and BC2 yielded ages of 1.33±0.23  Ma and 1.15±0.12  Ma, respectively (Ar 40   /  Ar 39 ages on plagioclases, Münch et al., 2013; 2014). These samples correspond to a prominent seismic reflector within the upper unit of the MG-MS3 sequence that can also be easily correlated through all the seismic lines west of Marie-Galante. We thus retain an average age of 1.29±0.26  Ma for this seismic reflector (green line in Fig. 4).

Figure 4 Seismic lines west of Marie-Galante (location in Fig. 3) showing the correlation across the Morne Piton fault system of the 1.29 Ma unit reflector (green) that corresponds to the reflector dredged at the BC1 and BC2 locations along the Ber03-30-31 seismic line. The 2.95 Ma unit boundary (red) is correlated with the seismic lines south of the Colombie bank and eastern Marie-Galante basin (line K09-90 and K09-26-62 location in Fig. 2). Notice that the basin sedimentary slope is in the E–W direction (parallel to line K08-14). Therefore, the initial topography of the reflectors in the N–S direction, across the fault system, can be neglected when measuring the offset along the seismic lines; uninterpreted profiles are provided in Supplement Fig. S1.

5.4  Tsunami modeling

In order to test the tsunamigenic potential of the fault system proposed herein, a rupture scenario is elaborated on and is presented hereafter.

Numerical simulations of tsunami generation and propagation were carried out using COMCOT software (Cornell Multi-grid Coupled Tsunami, Liu et al., 1998; Wang, 2008; Wang and Power, 2011). COMCOT is widely used by the research community and constantly tested notably through various real tsunami cases (e.g., Prasetya et al., 2011; Gusman et al., 2019; Paris et al., 2021; Gusman et al., 2022; Roger et al., 2023). COMCOT uses a modified staggered finite-difference scheme to solve linear and non-linear shallow-water equations in either spherical or Cartesian coordinate systems throughout a set of nested grids, allowing refinement of the bathymetric resolution in coastal areas. A two-way nested grid configuration is implemented in the model to balance computational efficiency and numerical accuracy (Wang, 2008; Wang and Power, 2011).

For this study, nesting was used with two grid levels: the first grid is a 0.5 arcmin ( ∼  900 m) resolution grid of the Lesser Antilles (extent: 295° E, 302° E, 12° S, 18° S) built from the global dataset GEBCO 2021 (GEBCO Compilation Group, 2021); the second grid is a 3.75 arcsec ( ∼  115 m) spatial resolution grid focusing on the Guadeloupe archipelago and Dominica island, including the location of the investigated Morne Piton fault system as shown in Fig. 1 (extent: 297.92° E, 300.22° E, 14.94° N, 16.717° N). This second grid was built from different datasets including the aforementioned bathymetric data (Sect. 5.2). The highest-resolution and most recent data were kept first. Data gaps were filled in with data from GEBCO (GEBCO Compilation Group, 2021) for offshore regions and SRTM version 3.0 global 1 arcsec data (NASA SRTM, 2013) for onshore regions. Continuity of the different datasets was ensured using kriging interpolation, which has proven to be one of the best methods to produce a well-defined DEM, especially for smooth transitions between different resolution areas (e.g., Bernardes et al., 2006; Arun, 2013; Ajvazi and Czimber, 2019). Note that Dominica was included in the second grid in order to look at potential effects which could occur between the different islands and also to assess the potential tsunami threat resulting from the Morne Piton scenario on this neighboring island.

The initial sea-bottom displacement is calculated by COMCOT considering an instantaneous rupture of the fault using the surface deformation model of Okada (1985), and transmission of the deformation to the water column above is considered to be instantaneous. Calculations of wave propagation were done at mean sea level (MSL) assuming a constant Manning roughness coefficient of 0.011 for the seabed friction (Wang et al., 2017). A higher friction coefficient leads to more energy dissipation of tsunami waves, especially in shallow waters, slowing down their speed and reducing their amplitude and impact (e.g., Dao and Tkalich, 2007). Considering the limited extent of the interest zone ( ∼  250 km  ×  200 km), the rupture parameters (leading to a small coseismic rupture) and the objective to look at the potential localized effect as inter-island resonance, tsunami wave propagation time was set to 10 h.

6.1  The Morne Piton fault system

The HR bathymetric data presented in Sect. 5.2 allow us to refine the structural pattern of the Morne Piton fault system, especially offshore (Fig. 3a–b). The fault system splays eastward from the N120–N135° E-trending eastern Les Saintes fault system located east-southeast of Basse-Terre to the N110–115° E-trending Petite-Terre fault system south-southeast of Grande-Terre (Figs. 2 and 3). Thus, the fault zone spreads over a 5–8 km wide and 50 km long zone with an average N100° E trend.

Morpho-bathymetric analysis allows us to identify surficial segments of the faults that are reaching the seafloor. The main fault scarp of the Morne Piton fault system is the southernmost one, along which 11 fault segments of 1–10 km length can be identified (Fig. 3b). From west to east, the F1 segment trends N110° E and then the fault steps left along the N75° E-trending F2 segment. A little farther east, the fault cuts the northern Colombie bank and the eastern Marie-Galante platform along closely spaced N90° E-trending left or right stepping segments F3, F3', F4 and F5. Across the island, the F6 segment is a N130° E-trending, 6 km long right step relay linking the F5 segment to the F7 N90° E-trending one. Further east offshore Marie-Galante, four N80° E-trending fault segments, F8, F9, F10 and F11, are arranged as overlapping right steps. There, the fault scarp vanishes in just a few kilometers. To the east of line Sis7C, neither the sediments nor the basement is affected by the north-dipping Morne Piton fault system (Fig. 5). In contrast, the seismic line Sis7C shows that the basement is southwardly downthrown by the Petite-Terre fault system, along south-dipping active and sealed faults to the north and south of the Morne Piton fault system, respectively (Fig. 5 location in Fig. 3a). West of Marie-Galante, the Morne Piton fault system widens as closely spaced fault splays trending N95° E to N100° E link the main fault scarp (F2, F3 and F4) to the antithetic Goyave fault system or die westward (Fig. 4 location in Fig. 3a). Eastward of the F6 segment, some synthetic and a few antithetic faults splay northeastward and link with the N110–115° E Petite-Terre fault system.

Figure 5 Seismic lines east of Marie-Galante illustrate the correlation across the Morne Piton fault system of the 7 Ma (Tortonian/Messinian) MG-SB3 sequence boundary (Purple) and the 16 Ma (Burdigalian) MG-SB2 sequence boundary (Orange). Seismic line location in Fig. 3; uninterpreted profiles are provided in Supplement Fig. S2.

The mean fault-scarp height west of Marie-Galante island is ca. 100 m (Fig. 3c). Across Marie-Galante island, the mean fault-scarp height reaches 200 m and controls the staircase morphology of the island. East of the island, the Marie-Galante canyon carved the sedimentary units, clearing some of the fault planes and increasing their apparent scarps heights up to 400 m. To the east, the canyon meanders and cuts through the eastern tip of the Morne Piton fault system (Fig. 3b and c). West of the island, in the vicinity of the volcanic island of Basse-Terre, either recent deposits or the uppermost sedimentary units seal most of the faults. These observations seem to indicate that the sedimentary rate west of Marie-Galante and the erosional rate east of Marie-Galante (in the canyon) exceed the vertical slip rate of the fault.

6.2  Vertical slip rate estimates along the Morne Piton fault system

To assess the average vertical slip rate along the Morne Piton fault system, we estimated the fault offset of key dated reflectors across the entire length of the fault system (Figs. 4 and 5; Table 2). West of Marie-Galante, the main offset of the 1.29  ±  0.26 Ma seismic reflector (green in Fig. 4) increases from west to east (i.e., from the westernmost extremity of the fault toward its center). Close to the eastern shore of Basse-Terre island (Fig. 4, profile K09-96, and Table 1), the 1.29 Ma reflector is downthrown by 110–115 m. Eastward, the reflector offset increases up to 230–257 m (Fig. 4, lines K09-90 and K08-24, and Table 2) and reaches a maximum of 300–322 m (Fig. 4, lines Ber03-30-31 and K08-59). Accordingly, the number of sealed structures across the fault system decreases eastward (Figs. 3 and 4). Thus, west of Marie-Galante, the Morne Piton fault system accommodates a vertical slip rate increasing eastward up to 0.25  ±  0.08 mm yr −1 over the last 1.29  ±  0.26 Myr (Table 2).

The 2.95  ±  0.05 Ma unit boundary (red line in Fig. 4) can only be correlated across the fault system along the K08-59 seismic line. Growth strata, characteristic of synsedimentary faulting, are observed in the deposits above the 2.95 Ma unit boundary (Fig. 4, gray shadow on seismic lines). This unit boundary offset reaches 550–620 m, leading to a 0.20±0.02  mm yr −1 average vertical slip rate over the last 2.95  ±  0.05 Myr, i.e., ca. 0.16 mm yr −1 for the period 2.95–1.29 Ma (Table 2). West of Marie-Galante island, deeper reflectors cannot be identified and correlated across the fault system because of the limited seismic penetration.

However, east of Marie-Galante, the MG-SB2 sequence boundary dated to 16±1  Ma (orange in Fig. 5; see also Fig. 5 in Cornée et al., 2023) is the only reflector that can be correlated on both sides of the fault system. In the hanging wall of the fault, the younger MG-SB3 7  ±  1.5 Ma boundary (Purple in Fig. 5) and a large part of the fault scarp are eroded by the Marie-Galante canyon. The seismic line K09-09 (Fig. 5) shows that the MG-SB3 unconformity records the Morne Piton fault inception: in the footwall of the fault, the stratigraphy of the MG-MS2 sequence (comprised between MG-SB2 and MG-SB3) shows conformal deposits flexed upward while approaching the fault, whereas MG-MS3 deposits onlap onto MG-SB3 and present clear growth strata. We thus propose that the 16  ±  1 Ma sequence boundary is pre-tectonic and is tilted by the fault since its inception at 7  ±  1.5 Ma (the age of MG-SB3; Fig. 5, profile K09-45-45). Along the fault system east of Marie-Galante, we calculated the strain rate from the MG-SB2 offset since 7±1  Ma. From east to west, the slip rate ranges from 0.067±0.03  mm yr −1 at the K09-44-45 seismic line to 0.071±0.02  mm yr −1 along the K09-08-09 line. Seismic line Agua97 (Fig. 5) presents the greatest offset of MG-SB2. However, this seismic line does not cross the southernmost F7 segment (the water depth is too shallow for ship navigation in the footwall compartment). We estimated the depth of MG-SB2 in the footwall compartment from the closest seismic line available that crosses the fault located 1 km east of the Agua97 line. We obtain an offset of 830–860 m, leading to a maximum average vertical slip rate of 0.12  ±  0.03 mm yr −1 since 7  ±  1.5 Ma, i.e., ca. 0.07 mm yr −1 for the period 7–2.95 Ma (Table 2). Consequently, we propose (i) that the vertical slip rate accommodated by the Morne Piton fault system increases progressively from each extremity of the fault toward its center and (ii) that the Morne Piton fault system is characterized by an increasing slip rate from ca. 0.07 from its inception (i.e., 7 Ma) to ca. 0.25 mm yr −1 since 1.29 Ma (Table 2).

6.3  Earthquakes parameters of tsunami modeling

ROV dive along the Ber03-30-32 seismic line allowed observation of one of the main morphologic scarps of the Morne Piton fault system across the F2 and F3' segments (Figs. 3 and 6). Across the upper plateau, between F2 and F3', we observed several N90° E-trending fractures parallel to the fault segments (Fig. 6a). While descending across the F3' scarp, the slope progressively steepens up from 45° at 157 m b.s.l. to more than 80° at 280 m b.s.l., just a few meters above the toe of the scarp (Fig. 6a, b and c). This morphology suggests a ca. 128 m high cumulative scarp for the F3' segment at that location. The very last meter of the fault scarp above the toe of the slope presents a 100 cm high polished vertical surface, partly altered, showing dip-slip striations indicating pure normal motion along this fault segment (Fig. 5d e and f). This exposed and partly altered fault slip plane breaches the seafloor at a high angle. Such a polished striated fault-scarp morphology is similar to, although more altered compared to, the coseismic fault scarp observed at the toe of the Roseau fault plane after the Les Saintes earthquake (Escartín et al., 2016). We conclude that this observation of the Morne Piton polished striated scarp may correspond to one of the last coseismic scarps formed during a major earthquake (including possible post-seismic slip motion) along this fault. Alteration of the fault slip plane suggests that the slip event occurred tens to several hundreds of years ago; i.e., this fault slip plane may correspond to a pre-instrumental earthquake (see Discussion). From this observed scarp, we obtained a ratio of the last scarp event over total scarp height (a proxy for the cumulative slip as determined in Fig. 3) of ∼  2.6 %. With this ratio we calculated an average scarp of ∼  75 cm along the whole length of the fault and a maximum scarp of 2 m. Such an average scarp value corresponds to the surface expression of a magnitude M w   ∼  6.7 earthquake using the criteria of Wells and Coppersmith (1994) or even M w   ∼  7 according to Thingbaijam et al. (2017). The same studies also provide a calculated maximum displacement of ∼  2 m, consistent with the maximum observation along the scarp. Moreover, the 45 km total length of the Morne Piton fault system measured from HR bathymetry, together with the width of the fault given by the 10 to 15 km thick seismogenic crust, leads to a rupture area ranging between ∼  450 and 675 km 2 that would generate a magnitude M w   ∼  6.7  ±  0.1 earthquake, corroborating the aforementioned range of magnitude deduced with other observations (e.g., M w  ranging between 6.6 and 6.8 according Wells and Coppersmith, 1994, and Leonard, 2010, and around 7 according to Thingbaijam et al., 2017). The rupture parameters for the different identified segments of the fault shown in Fig. 3b are provided in Table 3. The geographic locations of the center of the top of the fault plane and azimuth are provided based on our structural analysis (Sect. 6.1 and 6.3). Neither seismic lines which illustrate only a few hundred meters nor in-depth earthquake distributions (which are not resolved enough) allow us to estimate the dip of the Morne Piton fault system. Thus, after considering the influence of the dip on surface deformation, which turns out to be negligible, we choose a mean dip of 75° for the fault segments after Feuillet et al. (2004). The shape of the rupture area (along-strike length  ×  downdip width) and a slip of 1.89 m (maximum displacement estimated from scarp height measurement) is implemented for each segment in order to fit with a total fault surface of ca. 500 km 2 , corresponding to a magnitude M w  6.5 earthquake. Finally, in accordance with pure dip-slip striations observed along the F3' segment during the ROV dive (Fig. 6e), we apply a rake of 90°, corresponding to pure normal faulting. This is consistent with observations of dip-slip kinematic criteria made (i) along the F7 segment by Feuillet et al. (2002) and (ii) onshore at Anse Piton (Marie-Galante) by Feuillet et al. (2004). Fault segments F8 and F9 are not straight, and for the purpose of modeling they are divided into F8–F9 and F10–F11 (Fig. 7). Hereafter, we use these parameters to evaluate the potential tsunami hazard from the Morne Piton fault for a worst-case plausible scenario rupturing all the segments simultaneously.

Figure 6 ROV photographs of the fault identified on the seafloor along the Ber03-30-31 seismic line across the F3' Morne Piton fault segment (location in Fig. 3). (a)  Photography of the hanging wall of F3'. The eroded F3' fault plane presents a progressive downward slope steepening  (b, c) until the toe of the fault, which is marked by a characteristic coseismic scarp with dip-slip striae  (d, e, f) . In each panel, white numbers starting with a P represent the water depth in meters, latitude is north and longitude is west (WGS84). Panels  (a) , (b) and (c) show areas several tens of square meters wide; panels (d) , (e) and (f) are close-ups showing a ca. 1 m high escarpment just above the foot of the fault scarp (visible at the bottom of each panel).

Table 3 Parameters used for the tsunami source simulation of a rupture along the multi-segment fault presented in Fig. 7.

6.4  Plausible worst-case tsunami scenario and resulting hazard

We present a worst-case plausible scenario, related to a rupture along all the identified segments of the Morne Piton fault system as these 1 to 10 km long segments most probably root in depth along a single fault zone (Feuillet et al., 2004). We rule out the eventuality of testing a single 10 km long segment of the Morne Piton fault system rupture as it would generate a M w   <  6.0 earthquake and would thus unlikely consist of a tsunami source (e.g., Roger et al., 2019). Here, we use a plausible M w  6.5 scenario, i.e., a magnitude slightly lower that the maximum magnitude M w  6.7 deduced from the morphological analysis but close enough to the Les Saintes earthquake magnitude as both the Les Saintes and Morne Piton fault systems share close morphological characteristics. Our model would generate a tsunami with significant energy/amplitude to accurately highlight the potential consequences of tsunami waves' propagation and interaction with the peculiar shallow reliefs and major embayment located in and around the Marie-Galante basin. Quantifying horizontal run-up at the coast and assessing tsunami risk following a rupture along this fault is out of the scope of the present study, as such quantifications necessitate a better understanding of the fault dynamic itself (e.g., return period of large events).

The initial surface elevation directly resulting from the Okada's (1985) formulation is presented in Fig. 7. Due to the high inclination of the fault planes (dip  =  75°) dipping globally northward, a profile cut of the initial displacement is represented from the north to the south by a crest (positive elevation) and a trough (negative elevation). At t = 0, the shallow-water equations take over from this initial deformation, and the propagation of the tsunami waves is calculated over the nested grids at adequate time steps. Figure 8 presents the state of the virtual water surface at six different times of the tsunami wave propagation from 1 to 16 min. The wave front initially parallel to the fault axes ( t ≤1  min) is progressively influenced by the bathymetry within the very first minutes following the rupture, leading to an anisotropic propagation of the waves showing variability in space and time. In addition, the fact that the fault literally crosses Marie-Galante leads to the tsunami source being divided into two independent sources located in the west and east of this island: two tsunamis are therefore generated and called TsuW (in the west) and TsuE (in the east) hereafter. These two tsunamis propagate from their origin and wrap around Marie-Galante as shown at t =  4 min of propagation. Then, between 4 and 9 min, the two tsunami fronts meet on the north and south of Marie-Galante. Meanwhile, the propagation of the TsuW waves meets the shallow waters of the Colombie bank shoal (approx. coordinates: 15.98° N, − 61.43° W; minimum water depth is about 35 m) west of Marie-Galante: the waves' amplitude increases as they slow down, and their interaction leads to a constructive interference resulting in a new tsunami source at the Colombie bank shoal, mainly showing a negative wave propagating southward with some extensions toward Marie-Galante in the east and Les Saintes in the west.

Figure 7 Initial surface elevation for a maximum credible scenario built with the 11 fault segments detailed in Table 3. Blue dots indicate the top fault center. Acronyms stand for Grande-Terre (GT), Basse-Terre (BT), Les Saintes (LS) and Marie-Galante (MG).

Figure 8 Snapshots of tsunami elevation within the Guadeloupe archipelago at 1, 4, 8, 6, 12 and 16 min of wave propagation. Red and blue colors correspond to wave crests and troughs, respectively. The black arrow shows the Colombie bank shoal. BT: Basse-Terre; GT: Grande-Terre; S: Les Saintes; PT: Petite-Terre; MG: Marie-Galante.

Figure 9 Shadowed bathymetric map with tsunami maximum wave elevation. Numbered white dots: 14 virtual sea-level gauges (VG); BT: Basse-Terre; GT: Grande-Terre; S: Les Saintes; PT: Petite-Terre; MG: Marie-Galante; D: Dominica. VG_4 and VG_11 are located near the fault rupture region, and VG_5 and VG_6 are near the Les Saintes fault system. VG_1, VG_2 and VG_3 are within the Les Saintes archipelago.

Approaching the coasts, wave shoaling takes over, with the reduction in water depth slowing down the waves and simultaneously increasing their amplitude. It leads to wave amplification as particularly shown along the Marie-Galante north shore, the southeast coast of Basse-Terre, and the south of Petite-Terre and eastern Grande-Terre (Fig. 9).

After 10 h of tsunami propagation, the maximum values of wave amplitude reached on each point of the simulation domain are shown in Fig. 9. The overall impact of such an event is that the maximum wave amplitude is not going over 1.2 m, carefully considering the 100 m resolution of the simulation domain: in fact, grid refinement at the coast showing higher resolution would probably highlight higher wave amplitude in very localized areas because of interaction with small underwater structures not represented at this resolution, as well as non-linear effects. The patterns of those amplitudes indicate that not only the fault region but also some coastal regions are exposed to tsunami waves of 50 cm or more, which is above the usual beach and marine threat 30 cm threshold. It is the case for the neighboring coasts of Marie-Galante, southeast Basse-Terre, south Grande-Terre and the natural reserve of Petite-Terre. The southeast coast of Basse-Terre is particularly exposed, with wave amplitudes of more than 1 m (Fig. 9a). A focus on the Les Saintes archipelago also highlights wave amplitudes of more than 1 m, even between the islands (Fig. 9b). The northeast coast of Dominica is also affected but to a lesser extent (maximum wave amplitudes of ∼  50 cm). Further high-resolution simulation, including flow speed calculations, would help to correctly assess the related hazard on this island. Virtual sea-level gauges were added at different locations of grid 2 (Fig. 9) in order to check if the model is stable and to look for possible resonance (especially in the Les Saintes archipelago). The raw signal of seven VG (top Fig. 10) highlights a clear decrease in the amplitude over time in all stations. However, for stations VG_1, VG_2 and VG_3, a low-frequency oscillation is clearly visible and lasts for at least 10 h. The amplitude spectrums on these three stations show that two peaks with a period of ∼  8.5 and 15 min, respectively, are present on the three signals at Les Saintes, which is not the case for the stations out of the archipelago. Moreover, the high-amplitude negative wave southwardly propagating, generated by the new tsunami source at the Colombie bank shoal, is shown by VG_1 in Fig. 10, with a peak-to-trough value of ∼  0.6 m. VG_2 and VG_3 also show it to a lesser extent a bit later.

Figure 10 Post-processing of virtual gauge records. Top: sea-level records at seven different locations (VG_1 to VG_6 and VG_11; location in Fig. 9); bottom: single-sided Fourier amplitude spectrum. The black arrows symbolize the location of the two peaks with periods ∼  8.5 and 15 min.

Figure 11 Fault offset along the Morne Piton fault against the age of the strain marker. Red: data from Feuillet et al. (2004) based on absolute age of terrace T4 (MIS5e), the estimated age of terrace T2 (MIS7e) and the suggested age of the Marie-Galante upper plateau (MIS9e). Green: strain range calculated using the upper-plateau unit age from Münch et al. (2014) (note that erosion may lower this estimation strain rate). Blue: strain range calculated from the fault offset of the seismic unit dated ca. 1.2 Ma along the seismic line K08-59 (green reflector in Fig. 4). The dotted line indicates the 0.32 mm yr −1 strain rate from the estimated offset of the MIS5e terrace in Marie-Galante (Feuillet et al., 2004).

7.1  Upper-plate fault tsunamigenic potential

The Les Saintes earthquake demonstrated that upper-plate normal faults may generate M w   >  6 tsunamigenic earthquakes in the Lesser Antilles. The Les Saintes tsunami produced up to 2 m high waves at the coast and 42 m distance run-up in a peculiar embayment (Zahibo et al., 2005). Such normal faults are prone to be tsunamigenic because their rupture is relatively shallow (compared to the megathrust), and their slip motion is favorable to large seafloor displacement. Together with their proximity to the islands, they are able to produce meter-high tsunami waves at the coast and tens to hundreds of meters of run-up distances (depending on the topography). Therefore, upper-plate crustal faults may represent a major potential tsunami hazard in the Lesser Antilles islands and particularly in the Guadeloupe archipelago as pointed out by the Intergovernmental Oceanographic Commission held in Fort-de-France in 2019 (IOC-UNESCO, 2020). Similarly to the Les Saintes fault, we assume that the 50 km long Morne Piton fault poses a potential earthquake and tsunami hazard. The large scarp we observed at the toe of the Morne Piton fault suggests a recent seismogenic rupture(s) along this structure, which is potentially tsunamigenic. However, this scarp might not be related to the 1851 historical event as the estimated magnitude M w  5–5.5 for this earthquake appears too low to explain the observed scarp. Thus, a rupture of the fault along its whole length must not be excluded. Several other prominent onshore–offshore faults affect the seafloor and the topography of the archipelago and may represent both an earthquake and a tsunami hazard. However, the relationships between faults, earthquakes and tsunami is not clearly established as shown in the following examples.

Along the arc, the Montserrat–Havers–Bouillante and Les Saintes fault systems are the most prominent tectonic features (Feuillet et al., 2010). To the south, Les Saintes fault system dips east and defines a half graben (Leclerc et al., 2016). The westernmost fault, the Roseau fault, ruptured during the 2004 M w  6.3 earthquake and is most likely reloading stress and therefore quiet. The recurrence time for this earthquake was estimated to be more than 1000 years given the slow regional strain rate. However, the eastern normal faults of the system offset the seafloor over more than 30 km and present tilted blocks filled by fan-shaped Late Pleistocene deposits showing recent deformation. In the light of these observations, the eventuality of a tsunamigenic earthquake along these faults should be considered. To the northwest along the Havers segment, a rupture occurred in 1985, with a M w  6.5 earthquake showing strike-slip mechanisms. Beck et al. (2012) estimated a recurrence time of 6500–7000 years for such a M w  6.5 event based on the vertical offset of coseismic deposits in hemipelagites imaged by very high resolution seismic lines across the fault. In between these two segments, the Montserrat–Bouillante segment is seismically quiet except if the 1897 (estimated M w  7.0) earthquake occurred along this fault (Feuillet et al., 2011). However, no tsunami related to such a rupture has been reported. Seismic lines across the Montserrat–Bouillante fault (Feuillet et al., 2010; Legendre, 2018) reveal that the fault offsets the most recent units, including the oldest reflector drilled during the IODP1395 that dates to the upper Gelasian ca. 1.8–2 Ma (Le Friant et al., 2013). Given an offset of 0.3 m stwt and a 2000–2500 m s −1 sediment velocity, this provides a 0.15–0.2 mm yr −1 slip rate. Thus, the Montserrat–Bouillante segment should also be considered tsunamigenic (Fig. 2).

South of Grande-Terre of Guadeloupe, the N90° E-trending Gosier fault system bounds 45 km of coastal area (Fig. 2). The fault system offset the Middle Pleistocene Grande-Terre plateau that culminates at + 150 m from the offshore plateau that rests 15–20 m b.s.l. (Münch et al., 2013). This suggests a long-term vertical slip rate of ca. 0.10 mm yr −1 . To the east of Grande-Terre, the fault crosscuts the MIS5e terrace, showing the Late Pleistocene activity of the fault. However, evaluation of paleo-seismicity along one eastern segment of the fault system by means of trenches allowed the identification of recent surface ruptures, although superficial deposits remain undated (Terrier et al., 2002).

East of Guadeloupe, offshore, the Marie-Galante basin is bounded to the east by the Karukera spur (Fig. 2d), a 75 km long N–S-trending submerged plateau that culminates 30 m b.s.l. to the north offshore La Désirade island and gently dips southward down to ca. 1500 m b.s.l. (De Min et al., 2015). The spur is bounded to the west by N150° to N0° E-trending, west-dipping and normal faults. These faults offset the Middle Miocene sequence boundary (SB2) by up to ca. 2700–2900 m, leading to a long-term vertical slip rate of 0.16–0.18 mm yr −1 . Recent deposits are clearly affected by tectonic activity (Seibert et al., 2020). Located far from the islands, the earthquake intensity felt onshore would be relatively low in the island, but a tsunami could propagate across the Marie-Galante basin directly toward the coasts of the Lesser Antilles arc islands.

7.2  Slip rate reassessment along the Morne Piton fault system

With this study, we evidence that the slip rate along the Morne Piton fault system increases through time with a maximum slip rate of 0.25  ±  0,08 mm yr −1 over the last 1.29 Myr. This slip rate is up to 4 times slower than previous estimates. Over the last 330 kyr, Feuillet et al. (2004) estimate a bulk slip rate along the Morne Piton fault as high as 1 mm yr −1 over 330–125 ka and then decreasing to 0.3 mm yr −1 over the last 125 kyr. This last value is close to the long-term slip rate obtained offshore in this study (Fig. 11). These results suggest that the fault may present a fast slip rate during short periods of time (a few hundred kiloyears) separated by long periods (million years) of low slip rate. The fast 1 mm yr −1 rate was obtained considering that the terrace T2MG is offset by the fault by 159 m and dates to MIS7e (249 ka), and the upper plateau of Marie-Galante corresponds to an abrasion surface from the MIS9e high stand (330 ka; Feuillet et al., 2004).

This latter statement can be reconsidered. The same Agaricia  sp. limestone unit and Acropora  sp. limestone unit top the three islands, Grande-Terre, La Désirade and Marie-Galante, suggesting they emerged synchronously (Feuillet et al., 2002; Cornée et al., 2012; Münch et al., 2013). In the three islands, the youngest formation, the Acropora unit, is not younger than 1.07 Ma and not older than 1.54 Ma (Cornée et al., 2012; Münch et al., 2014). From the geological map of Bouysse et al. (1993), this unit rims the Marie-Galante island. In La Désirade, the upper-plateau culminates at 276 m a.s.l. (above sea level), whereas the 330 ka terrace is at 35 m a.s.l. (Lardeaux et al., 2013; Leticée et al., 2019). Consequently, the hypothesis stating that the plateau emerged at 330 ka can be ruled out in Marie-Galante. Based on the age of the latest deposit of the Marie-Galante plateau that ranges between 1.54 and 1.07 Ma, a vertical slip rate of 0.15–0.22 mm yr −1 can be calculated. This value is close to the ca. 0.25 mm yr −1 obtained offshore for the slip rate along the Morne Piton fault system over the same period of time (Fig. 11). As a consequence, it is not possible to conclude that the Morne Piton fault system has short periods of a fast slip rate, but instead it probably increases through time, reaching a maximum slip rate of 0.25 mm yr −1 over the last million years. As a consequence, dividing the slip rate along the Morne Piton fault system by four increases the earthquake time recurrence along this fault system and thus the time recurrence of potential associated tsunamis. Constraining the fault slip rate at the timescale of one seismic cycle or a few seismic cycles may allow for better estimates of seismic and tsunamigenic hazards of the Morne Piton fault system. This would require a better understanding of in-depth fault geometry and identification of its active segments, which could be obtained by means of a microseismic survey (using ocean-bottom-seismometer acquisition over 1–2 years or more). In the present day, BOTDR (Brillouin Optical Time Domain Reflectometry) laser reflectometry is used to perform long-term monitoring of the Morne Piton fault using the network of submarine telecom fiber optic cables connecting Marie-Galante to the larger islands of Basse-Terre and Grande-Terre (Gutscher et al., 2023). It should be noted that given the slow strain rate and in the absence of rupture occurring along the fault during the survey period, identifying the slip rate across this fault system may require hundreds to thousands of years. Moreover, very high resolution seismic data across the fault in areas of high sedimentation rates (i.e., along the eastern coast of Basse-Terre island) may constrain the Holocene fault activity. Slip rate estimates can be obtained by coring and dating of (i) the most recent deformed sediments as well as (ii) tsunami deposits in salt marshes. Finally, such regional monitoring would also contribute to a survey of past and potential landslides that may also be induced by earthquakes and which may locally generate destructive waves.

7.3  Bathymetric feature control of tsunami wave propagation

The aim of the tsunami simulation associated with the present study is not to produce a precise hazard assessment for the islands of Guadeloupe but rather to give an overview of what could happen in terms of tsunami generation if all the identified segments of the Morne Piton fault system ruptured together and to identify a few gaps in terms of scientific knowledge and operational activities. An accurate hazard assessment study would require many rupture scenarios, including combinations of the segments used in this study, with variations in their parameters and sensitivity tests.

The main outcome of the simulation presented above lies in the fact that submarine features play an important role in the tsunami wave behavior and amplitude. Submarine canyons are known to focus the waves (e.g., along the continental slope of the middle American trench, Álvarez-Gómez et al., 2012; or at Nazarè, Portugal, Martins et al., 2010; do Carmo et al., 2022; Delpey et al., 2021). This behavior also occurs along the rim of the island submarine plateau, raising the wave amplitude as exemplified in front of the most populated cities of southeastern Grande-Terre (Fig. 9). Shallow-water plateaus located around or between islands slow down the waves, which leads to particular propagation patterns like the wrapping around the relief (Fig. 8). There, the wrapping effect of the waves around Marie-Galante and the Colombie bank result in two distinct tsunami sources, i.e., a primary source at the fault and a secondary one at the Colombie bank (Fig. 8). Such a behavior, already shown in other regions, is able to considerably amplify the impact of the tsunami on the coast opposite to the fault rupture (Chadha et al., 2005; Chen et al., 2012). It is important to notice that the low resolution of the grid used for the present simulations is a limiting factor in quantifying correctly the wave amplitude along the shoreline. A higher-resolution simulation grid would better reproduce the bathymetric features, especially in shallow waters, having a non-negligible impact on the waves' behavior and amplitude.

Our simulation also highlights interesting phenomena that would require further consideration in the framework of further tsunami hazard studies: wave oscillation, which could be attributed to a resonance effect, is clearly visible within the Les Saintes archipelago, and potential wave trapping is also visible around those islands. If the second case is purely observation, the resonance between the Les Saintes islands is clearly revealed by the single-sided Fourier amplitude spectrum (Fig. 10), and the peak at ∼  15 min seems to be associated with the negative wave coming after the initial wave front and related to the tsunami interaction with the Colombie bank shoal. The records provided by the virtual gauges located beforehand within the archipelago (VG_1, VG_2 and VG_3) clearly show a long-period oscillation of the signal which is not present on the gauges located outside of Les Saintes (VG_4, VG_5, VG_6 and VG_11). It shows how the frequency content of the incoming signal can affect the sea level for many hours after the seismic rupture.

The numerical simulations performed by Cordrie et al. (2020) of the tsunami following the M w  6.3 Les Saintes earthquake were able to match the witnesses' observations in Les Saintes (Zahibo et al., 2005). Despite the low resolution (100 m) of the present simulation on Les Saintes, there are some similarities between the two studies of potential impacted zones, for example, in the Marigot or Grande-Anse bays. It also shows that other bays, like the ones located between Terre-de-Haut and Îlet à Cabrit, appear to be quite well protected and are not exposed to relatively strong tsunami waves.

Finally, this study also highlights the exposed coastline of Dominica: on the north-northeast coast of the island (Fig. 9), 50 +  cm waves are simulated, showing that this island should integrate such a scenario of crustal fault rupture within its tsunami hazard assessment plan.

Thanks to HR bathymetry, reflection seismic data and sediment samples, the analyses of the morphology and tectonic structures of the Marie-Galante basin located in the middle of the Guadeloupe archipelago allow us to detail the structural pattern of this region and to estimate a slip rate of ca. 0.1 mm yr −1 increasing over the last million years to 0.25 mm yr −1 , along the Morne Piton fault system, crosscutting the basin. This estimate divides the previously published estimations of the slip rate by four and thus increases the earthquake recurrence time associated with the Morne Piton fault system from 1 to 4–5 kyr. We show that a seismic rupture associated with an earthquake showing a moment magnitude M w   ∼  6.5 can occur along the Morne Piton fault system in the event of a rupture of the full length of the fault (with all segments being considered connected at depth in the present demonstration). Such an event would be tsunamigenic according to numerical simulation results. The multi-segment tsunami modeling illustrates how submarine morphological and structural features influence the propagation pattern of the tsunami, leading to interference and resonance and an increase in the tsunami threat on nearby islands. It also highlights a resonance effect within the Les Saintes islands which has not been discussed and may be a potential explanation for the so-far unreproduced run-up values of the 2004 tsunami. At a regional scale we evidenced that several other regional faults, such as the Montserrat–Havers–Bouillante fault, the Gosier fault and the Karukera spur border fault, may also be tsunamigenic. Indeed, although they have the potential to produce relatively low magnitude ( <  7) earthquakes, their rupture could occur at shallow depth and close to a highly populated coast. Therefore, scenarios with arc and forearc crustal fault ruptures must be integrated within their tsunami hazard assessment plan. For that, it is necessary to have a better understanding of onshore–offshore structural and seismogenic patterns of each individual major faults system as the regional low strain rate leads to a large recurrence time of tsunamigenic earthquakes ( >  1000 years), i.e., much greater than the historical record. In addition, these earthquakes could also have the capacity to destabilize the sedimentary layers at the edge of plateaus and canyons, triggering submarine mass failures, and are also capable of triggering large but more localized tsunamis.

Litto3D data can be found at https://services.data.shom.fr/geonetwork/srv/fre/catalog.search#/metadata/BATHYMETRIE_LITTO3D_GUAD_2016.xml (Shom-IGN, 2019).

French oceanographic fleet data can be obtained on demand via the Sismer online interface following the cruise DOI for Aguadomar, https://doi.org/10.17600/98010120 (Deplus, 1998); Sismantilles, https://doi.org/10.17600/1080060 (Hirn, 2001) and https://doi.org/10.17600/7010020 (Laigle et al., 2007); and KaShallow, https://doi.org/10.17600/9020010 (Lebrun, 2009).

Requests for the GEOBERYX03 data must be addressed to the BRGM.

Some figures were prepared using the Generic Mapping Tools version 6 software ( https://www.generic-mapping-tools.org , Wessel et al., 2019).

The supplement related to this article is available online at:  https://doi.org/10.5194/nhess-24-3129-2024-supplement .

MP: conceptualization; investigation; visualization; data curation; formal analysis; methodology; writing (original draft); writing (review and editing). JR: conceptualization; investigation; data curation; formal analysis; methodology; writing (original draft); writing (review and editing). JFL: formal analysis; investigation; resources; writing (review and editing). IT: formal analysis; investigation; resources; writing (original draft); writing (review and editing). OF: validation; writing (review and editing). SM: validation; writing (review and editing). MAG: investigation; validation; writing (review and editing). LM: resources; writing (review and editing). JJC: conceptualization; investigation; writing (original draft); writing (review and editing).

The contact author has declared that none of the authors has any competing interests.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors.

We are grateful to Cecile Deplus (IPGP), Alfred Hirn (IPGP) and Mireille Laigle (GeoAzur) for providing Aguadomar and Sismantilles seismic and bathymetry data and to Isabelle Thinon and Pol Gennoc (BRGM) for providing the GEOBERYX03 seismic data. We warmly thank José A. Álvarez-Gómez and the anonymous reviewer for their constructive comments and the editor Rachid Omira for handling our paper.

The KaShallow project was supported by the French national program DyETI from INSU-CNRS and by the European Interreg IIIB “Caribbean Space” fund engaged in Guadeloupe with the European Regional Development Fund (ERDF) projects (op. 30-700) and the region of Guadeloupe. Jean Roger has received financial support from the New Zealand's Strategic Science Investment Fund (SSIF). Melody Philippon has received financial support from the ANR SUBUTTEC, ANR-23-CE01-0028.

This paper was edited by Rachid Omira and reviewed by José A. Alvarez-Gómez and one anonymous referee.

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• Introduction
• Geological settings
• Historical seismicity
• Historical tsunamis
• Material and method
• Conclusions
• Code and data availability
• Author contributions
• Competing interests
• Acknowledgements
• Financial support
• Review statement

A Case Study on the Effect of Multiple Earthquakes on Mid-rise RC Buildings with Mass and Stiffness Irregularity in Height

• Research Paper
• Published: 17 September 2024

Cite this article

• Pavan Kumar Thippa 1 ,
• R. K. Tripathi 1 &
• Govardhan Bhat 1  

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Irregularities present in buildings play a crucial role when subjected to earthquake loads. In this study, an existing Reinforced Concrete (RC) structure is considered, which is designed and constructed without considering irregularity and seismic load effect. Due to functional requirements and usage of the floor for other occupancy purposes, columns were removed, which resulted in stiffness irregularity, and the imposed load difference resulted in mass irregularity at the same storey level. Three types of structures were analyzed and compared to understand the seismic effects and collapse probability of induced irregularity in existing RC structures. The main goal of this study is to find out how multiple earthquakes affect the induced irregularity in structures. To assess the performance of the structures, Incremental Dynamic Analysis (IDA) is performed, and fragility relationships are generated with and without irregularities for both single and multiple earthquakes. The results are compared in terms of Inter-storey Drift Ratio (IDR), roof displacement, and probability of collapse for three framed structures. The analytical study identifies that the effect of multiple earthquakes has a crucial impact on irregular structures. The irregular structure’s median storey drift has been observed to have attained the maximum drift threshold of 4% as per FEMA 273.The findings highlight the importance of analyzing the structures subjected to multiple earthquakes. The results indicate that multiple earthquakes are significant and should be considered in the analysis phase to avoid the collapse of regular and irregular structures. Introducing irregularity into structures already constructed should be avoided.

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Seismic evaluation of non-seismically detailed RC buildings in Pakistan: performance and damage accumulation under repeated earthquakes

Incremental Dynamic Analysis of Geometrically Irregular RCC Buildings

Seismic response of irregular RC buildings designed for gravity and seismic loads

Data availability.

No datasets were generated or analysed during the current study.

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Acknowledgements

The writers express their profound gratitude to the Ministry of Education (MoE) and the National Technology Institute Raipur (NITRR), India, for providing essential assistance in carrying out their research.

The authors affirm that they had no financial assistance from outside for the purpose of conducting the research work.

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Pavan Kumar Thippa, R. K. Tripathi & Govardhan Bhat

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Every author has enriched the current study at every step of the paper. Pavan Kumar Thippa handled the data collecting, analysis, and preparation of paper. Dr. R K Tripathi and Dr. Govardhan Bhat provided the guidance and resources required for the investigation. The final version has been approved by all writers.

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Appendix A. Validation of Numerical Model

The current work predicted the seismic response of reinforced concrete frame buildings using a concentrated nonlinear two-dimensional numerical model. Utilizing Sap2000, an analytical model is developed. For beams and columns, the member modelling use a degrading hysteretic model, and the P-Δ effect has been considered. Models of flexural hinges for beams and columns elements have been generated. The nonlinear analytical model has been validated using experimental data from Filiatrault et al. ( 1998 ) on a moment-resisting frame subjected to seismic load. Further information about the section properties, applied loading of the frame, and material properties can be obtained from Filiatrault et al. ( 1998 ). The Western Washington earthquake of April 13, 1949, time history component N04W of the accelerogram recorded in Olympia, Washington, is used in performing time history analysis. The reported peak horizontal acceleration of 0.16 g is scaled up to 0.21 g to calculate the seismic responses.

Base shear, and drift ratio from the numerical model has been compared with the experimental observations in Tables 16 and 17 . The percentage difference in base shear is found to be decreased by 8.31% for analytical results in comparison with experimental results. The percentage difference in storey drift is found to be increased by 8.59% on the first floor and 9.09% on the second floor for analytical results in comparison with experimental results. It is observed that there is a significant correlation between the numerical and experimental results, indicating that the nonlinear analytical model employed in this study is capable of accurately predicting nonlinear responses.

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Thippa, P.K., Tripathi, R.K. & Bhat, G. A Case Study on the Effect of Multiple Earthquakes on Mid-rise RC Buildings with Mass and Stiffness Irregularity in Height. Iran J Sci Technol Trans Civ Eng (2024). https://doi.org/10.1007/s40996-024-01625-0

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Received : 02 June 2024

Accepted : 07 September 2024

Published : 17 September 2024

DOI : https://doi.org/10.1007/s40996-024-01625-0

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Case Study – The 2011 Japan Earthquake

Cambridge iGCSE Geography > The Natural Environment > Earthquakes and Volcanoes > Case Study – The 2011 Japan Earthquake

Background Information

Location : The earthquake struck 250 miles off the northeastern coast of Japan’s Honshu Island at 2:46 pm (local time) on March 11, 2011.

Japan 2011 Earthquake map

Magnitude : It measured 9.1 on the Moment Magnitude scale, making it one of the most powerful earthquakes ever recorded.

Japan is a highly developed country with advanced infrastructure, technology, and a robust economy. The nation has a high GDP, an efficient healthcare system, and extensive education. However, it’s also located in the Pacific Ring of Fire, making it prone to earthquakes.

What caused the 2011 Japan earthquake?

Japan is located on the eastern edge of the Eurasian Plate. The Eurasian plate, which is continental, is subducted by the Pacific Plate, an oceanic plate forming a subduction zone to the east of Japan. This type of plate margin is known as a destructive plate margin . The process of subduction is not smooth. Friction causes the Pacific Plate to stick. Pressure builds and is released as an earthquake.

Friction has built up over time, and when released, this caused a massive ‘megathrust’ earthquake. The enormous tension released as the plates shifted caused the seafloor to uplift, triggering the earthquake and subsequent tsunami .

The amount of energy released in this single earthquake was 600 million times the energy of the Hiroshima nuclear bomb.

Scientists drilled into the subduction zone soon after the earthquake and discovered a thin, slippery clay layer lining the fault. The researchers think this clay layer allowed the two plates to slide an incredible distance, some 164 feet (50 metres), facilitating the enormous earthquake and tsunami.

The earthquake occurred at a relatively shallow depth of 20 miles below the surface of the Pacific Ocean. This, combined with the high magnitude, caused a tsunami (find out more about  how a tsunami is formed  on the BBC website).

What were the primary effects of the 2011 Japan earthquake?

• Ground Shaking : Extensive damage to buildings and infrastructure.
• Landfall: Some coastal areas experienced land subsidence as the earthquake dropped the beachfront in some places by more than 50 cm.

What were the secondary effects of the 2011 Japan earthquake?

• Tsunami : A giant tsunami wave resulted in widespread destruction along the coast.
• Fatalities : Around 16,000 deaths were reported, mainly resulting from the tsunami.
• Injuries : 26,152 were injured, mainly as a result of the tsunami.
• Nuclear Crisis : The Fukushima Daiichi nuclear power plant was damaged, leading to radiation leaks.
• Economic Loss : Estimated at over $235 billion.
• Displacement : Around 340,000 people were displaced from their homes.
• Damage: The tsunami destroyed or damaged 332,395 buildings, 2,126 roads, 56 bridges, and 26 railways. Three hundred hospitals were damaged, and 11 were destroyed.
• Environmental Damage : Coastal ecosystems were heavily impacted.
• Blackouts: Over 4.4 million households were left without electricity in North-East Japan.
• Transport: Rural areas remained isolated for a long time because the tsunami destroyed major roads and local trains and buses. Sections of the Tohoku Expressway were damaged. Railway lines were damaged, and some trains were derailed.

What were the immediate responses to the 2011 Japan earthquake?

Tsunami Warnings and Prediction :

• The Japan Meteorological Agency issued tsunami warnings three minutes after the earthquake.
• Scientists predicted where the tsunami would hit using modelling and forecasting technology.

Search and Rescue Operations:

• Rescue workers and 100,000 members of the Japan Self-Defence Force were dispatched within hours.
• Some individuals were rescued from beneath rubble with the aid of sniffer dogs.

Radiation Protection Measures:

• The government declared a 20 km evacuation zone around the Fukushima nuclear power plant.
• Evacuees from the area around the nuclear power plant were given iodine tablets to reduce radiation poisoning risk.

International Assistance:

• Japan received help from the US military.
• Search and rescue teams from New Zealand, India, South Korea, China, and Australia were sent.

Access and Evacuation:

• Access was restricted to affected areas due to debris and mud, complicating immediate support.
• Hundreds of thousands were evacuated to temporary shelters or relocated.

Health Monitoring :

• Those near the Fukushima Daiichi nuclear meltdown had radiation levels checked and their health monitored.
• Measures were taken to ensure individuals did not receive dangerous exposure to radiation.

What were the long-term responses to the 2011 Japan earthquake?

Reconstruction Policy and Budget:

• Establishment of the Reconstruction Policy Council in April 2011.
• Approval of a budget of 23 trillion yen (£190 billion) for recovery over ten years.
• Creation of ‘Special Zones for Reconstruction’ to attract investment in the Tohoku region.

Coastal Protection Measures:

• Implementing coastal protection policies like seawalls and breakwaters designed for a 150-year recurrence interval of tsunamis.

Legislation for Tsunami-Resilient Communities:

• Enactment of the ‘Act on the Development of Tsunami-resilient Communities’ in December 2011.
• Emphasis on human life, combining infrastructure development with measures for the largest class tsunami.

Economic Challenges and Recovery:

• Japan’s economy wiped 5–10% off the value of stock markets post-earthquake.
• Long-term response priority: rebuild infrastructure, restore and improve the economy’s health.

Transportation and Infrastructure Repair:

• Repair and reopening of 375 km of the Tohoku Expressway by the 24th of March 2011.
• Restoration of the runway at Sendai Airport by the 29th of March, a joint effort by the Japanese Defence Force and the US Army.

Utility Reconstruction:

• Energy, water supply, and telecommunications infrastructure reconstruction.
• As of November 2011: 96% of electricity, 98% of water, and 99% of the landline network had been restored.

How does Japan prepare for earthquakes, and what was its impact?

Japan has a comprehensive earthquake preparedness program, including:

• Strict Building Codes : Buildings are constructed to withstand seismic activity.
• Early Warning Systems : Advanced technology provides early warnings to citizens.
• Education and Drills : Regular earthquake drills in schools, offices, and public places.

Impact of the 2011 Earthquake

The extensive preparation in Japan likely saved lives and reduced damage during the 2011 earthquake. However, the unprecedented magnitude of the event still led to significant destruction, particularly with the tsunami and nuclear crisis.

The 2011 Japan earthquake illustrates the complexity of managing natural disasters in even the most developed and prepared nations. The event prompted further refinements in disaster preparedness and response in Japan and globally, highlighting the need for continuous assessment and adaptation to seismic risks.

The 2011 earthquake occurred off Japan’s Honshu Island, measuring 9.1 on the Moment Magnitude scale, one of the strongest ever recorded.

Triggered by a ‘megathrust’ in a destructive plate margin, the Pacific Plate subducted the Eurasian Plate, releasing energy equivalent to 600 million Hiroshima bombs.

Primary effects included extensive ground shaking and significant land subsidence in coastal areas.

Secondary effects included a massive tsunami, around 16,000 deaths, 26,152 injuries, a nuclear crisis at Fukushima, over $235 billion in economic loss, displacement of 340,000 people, and widespread damage to infrastructure and the environment.

Immediate responses included rapid tsunami warnings, extensive search and rescue operations, radiation protection measures, international assistance, and evacuation strategies.

Long-term responses focused on reconstruction policies, coastal protection, tsunami-resilient community development, economic recovery, and transportation and utility restoration.

Japan’s extensive earthquake preparedness, including strict building codes and early warning systems, likely reduced damage, but the magnitude still caused significant destruction.

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