New Seismotectonic Zoning Model for Seismic Hazard Assessment of the Lesser Antilles
Résumé
Seismic hazard levels used as reference for the French Lesser Antilles are derived from
probabilistic seismic hazard assessment studies performed in 2002. However, scientific
knowledge has greatly increased over the past 20 years in this area, warranting an update of the seismic hazard models. As part of a project linking the French Ministry of Ecological Transition and Territory Cohesion, and the Seismicity Transverse Action of RESIF-EPOS (French seismological and geodetic network), we developed a new seismotectonic zoning model of the Lesser Antilles. The Lesser Antilles tectonic system results from the subduction of the North and South American plates beneath the Caribbean plate since the Eocene. The boundary extends along 850 km with a convergence of 18-20 mm/yr oriented ENE-WSW. Significant north-south variations in tectonics, seismic and volcanic activities highlight the lateral variability of the undergoing geodynamic processes. Oceanic fractures and ridges entering into the subduction zone impact the trench, the subduction interface, and upper plate tectonics, adding seismotectonic complexities. Several controversial questions remain, such as the origins of the 1839 (Mw=7.5-8) and 1843 (Mw=8-8.5) earthquakes or the state of interseismic coupling of the subduction interface (potentially very low compared to other subduction systems). In this study, we propose new seismotectonic models and associated seismotectonic zoning for seismic hazard. We treat all components of the Lesser Antilles system: subducted oceanic plate, subduction interface, mantle wedge, upper plate crust and associated volcanisms. Our work is based on a compilation of up-to-date seismicity and fault catalogs as well as research-based active tectonic hypotheses, completed by an analysis of focal mechanisms rupture styles and strain tensor derived from geodetic data. Compared to previously published models, our new seismotectonic zoning model provides better depth resolution, a fully revised zoning around Guadeloupe, new mantle wedge and volcanic zones, and a complete redefinition of the subduction interface and slab. Our results also highlight specific needs for better seismic hazard assessment in this region.
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