Long Term Recurrence of Deeply Ponded Turbidites and Thick Homogenites in the Lesser Antilles Forearc: Imprint of Great Earthquakes
Abstract
As a subduction zone, the Lesser Antilles arc's islands are threatened by large magnitude earthquakes located at the interface between the American plates and the Caribbean plate. However, the short-term earthquake catalog has not recorded megathrust earthquakes. Only two major events were reported in January 11, 1839 and February 8, 1843, destroying the main cities in Martinique and Guadeloupe, respectively. To improve our knowledge of the seismic hazard of the arc, the search for geological traces of such earthquakes has been developed by focusing on sedimentary recording. During the CASEIS cruise, giant piston cores were collected to perform a submarine paleoseismological study based on shock-induced gravity reworking and other subsequent effects of tsunami-induced sedimentary processes (mass transport deposits, turbidites, homogenites). This study is focused on the surrounding area of the 1843 earthquake estimated rupture, in the forearc basins confined between the arc basement offshore the Guadeloupe island and the accretionary wedge.
A multiproxy approach combining geophysical, geochemical and sedimentological data was performed on six cores. The ages of gravity deposits are estimated from radiocarbon ages and biostratigraphy provided on one core. Sedimentological features can be used to exclude other sources (variable provenance of sediment, multi-pulse turbidite deposits) and a wide spatial extent of synchronous turbidite deposition is recognized as the most likely signature of large earthquakes. We propose a correlation of the turbidite deposits throughout the forearc basins based on the stratigraphic characteristics of the cores, the sediment facies and the radiocarbon ages. Based on all parameters and high-resolution seismic profiles, correlations of 33 events have been established between separated sites over the last 120 ky, including 4 thick gravity reworking events identified as up to 5 m-thick "turbidites+homogenites". The 1843 earthquake was not identified in the cores. Thus, it implies that the deposits were triggered by greater or shallower megathrust earthquake. Their mean recurrence interval is roughly 3200 years (up to 12000 years). The homogenite deposits seem related to more processes controlling the particle settlement which could be a tsunami wave.- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMOS51C1503S
- Keywords:
-
- 3045 Seafloor morphology;
- geology;
- and geophysics;
- MARINE GEOLOGY AND GEOPHYSICS;
- 3070 Submarine landslides;
- MARINE GEOLOGY AND GEOPHYSICS;
- 4313 Extreme events;
- NATURAL HAZARDS;
- 7221 Paleoseismology;
- SEISMOLOGY