large earthquakes and tsunamis in the Lesser Antilles arc: impact on coastal and deep offshore sedimentation, reef growth and human settlement – CARQUAKES

Megathrust earthquakes can induce metric-scale sudden subsidence or uplift, and destabilize shelf sediments, instigating turbiditic flows and landslides. They can also generate tsunamis that can transport huge quantities of marine and coastal sediments and debris inland. Such dramatic events can cause many casualties, destroy infrastructure, and have longer-term impacts on the environment. They may considerably modify the landscape, affecting human settlement over millennia. Between large earthquakes, due to strain accumulation, land deformation induces relative sea level changes at rates much faster than those due to climate change. These events represent a major threat and must be accounted for in regional planning. Missing information on such extreme and rare events, necessary to better constrain the seismic hazard, is a major limitation. The largest earthquakes may recur only every 500 or 1000 yrs and the historical catalogs are too short to allow an estimation of earthquake recurrence intervals and of their magnitude. Existing models based on short historical records have not been successful at predicting earthquake recurrence. Paleoseismological and paleotsunami studies of the geological record are thus needed to address this issue and establish time series over thousands of years.
The Lesser Antilles arc is a densely populated and highly touristic zone exposed to megathrust earthquakes. The largest historical event that occurred on 8 February 1843t destroyed the city of Pointe-à-Pitre on Guadeloupe, killing more than 1500 people. Today, a comparable earthquake might cause tens of thousands of casualties.
The objective of the CARQUAKES project is to improve the catalog of large earthquakes and tsunamis in the Lesser Antilles and characterize the related hazards by applying an innovative and novel multidisciplinary approach combining several state-of-art methods of offshore and onshore paleoseismology and tsunami modeling. Offshore, we will use the marine sediments (i.e. turbidites/homogenites) as proxies for earthquake recurrence in the Lesser Antilles (Task 1). During the CASEIS marine cruise in Spring 2016, we collected 42 sedimentary cores in the eastern part of the Lesser Antilles arc, above the megathrust zone. The CARQUAKES project is in part conceived to permit the exploitation of this large dataset. Onshore, we will combine several approaches to retrieve the traces of extreme events: 1) paleoseismological and paleotsunami studies in coastal lagoons and ponds that may have preserved the evidence of earthquakes and tsunamis (Task 2); 2) Coral paleogeodesy along the reefs, where coral microatolls may record earthquakes in their skeletal growth (Task 3); and 3) Archaeology and history comprising analysis of historical descriptions of earthquakes and tsunamis in archives and investigations of several coastal archeological sites on Guadeloupe (Task 4). Tsunami and strain modeling will be performed to calculate the impact of earthquake cycle and tsunamis on the littoral zone (wave height, inundation and coastline variations) (Task 5). The CARQUAKES project brings together experts in tectonics, geomorphology, paleoseismology and paleotsunamis, sedimentology, paleo-environment, tsunami modeling, botany, palynology, archaeology, and history. Six partners are involved in the project. The project will benefit society because it will provide information essential to reduce the vulnerability of coastal populations in the Lesser Antilles islands. This will improve our knowledge of earthquake and tsunami hazards and their impact on coastline evolution, ecosystems (destruction and resilience) and human settlement.