Elements of the Seismic Structure and Activity of the Lesser Antilles Subduction Zone (Guadeloupe and Martinique Islands) from the SISMANTILLES Seismic Survey
Abstract
The Lesser Antilles is an active subduction zone, prone to future major earthquakes as it has experienced in the past with the occurrence in 1843 of a M>7.5 probably mega-thrust earthquake that destroyed Pointe-a-Pitre city on Guadeloupe Island. The SISMANTILLES project was carried out at a regional scale for a first reconnaissance of the seismic structure and activity from northern Guadeloupe to Martinique islands. The project focused more particularly on the detection, mapping and characterisation of the potentially seimogenic part of the interplate subduction fault. The french N/O Nadir vessel acquired 2500 km of deep-penetration multichannel reflection seismic (MCS) profiles. Up to 37 3-components Ocean Bottom Seismometers (OBS) were deployed offshore over several weeks together with a set of 3-components broadened-band stations on the islands (Martinique, Dominica, Guadeloupe and Antigua). These instruments recorded continuously both the MCS shots that provided wide angle reflexion and refraction (WARR) data as well as the local, regional and teleseismic earthquakes. On MCS profiles, reflections from the top of the subducting oceanic crust and decollement can be followed down to several km depth beneath the thick accretionary prism. Detailed velocity analysis provided depth structural sections that are used as an input for the forward modeling of WARR data. Thanks to these data, we can constrain on 3 transects to the arc, the part where the forearc deep crust is in contact with the subducting oceanic plate, considered as a proxy for the seismogenic part. Its location with respect to the deformation front and the volcanic arc and its downdip size appear significantly variable along the arc. The local earthquakes now reliably located in map and depth thanks to the high-quality P and S observations of the OBS network can be discussed with respect to these imaged structures. Local earthquakes P & S tomography as well as receiver functions analysis will bring more constraints on the deeper structure beneath the arc crust and thus on the downdip limit of the seismogenic portion of the subduction interplate.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2005
- Bibcode:
- 2005AGUFM.T33C0580L
- Keywords:
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- 0468 Natural hazards;
- 1734 Seismology;
- 3025 Marine seismics (0935;
- 7294);
- 7230 Seismicity and tectonics (1207;
- 1217;
- 1240;
- 1242);
- 7240 Subduction zones (1207;
- 1219;
- 1240)