Future magnitude 7.5 earthquake offshore Martinique: Spotlight on major source-related factors of ground-motion variability

The eastern offshore of Martinique is one of the active areas of the Lesser Antilles Subduc tion Zone (LASZ). Although its seismicity is moderate compared to other subduction zones, LASZ is capable of generating a M 7+ interplate earthquake and recent studies and historical events, such as the M8 1839 and M 7-7.5 1946 earthquakes, confirm this possibility. Given the high risk that Martinique can face in case of unpreparedness for such a M 7+ earthquake, and the lack of a regional seismic hazard study, we investigated through numerical modelling the ground motion variability for a hypothetical Mw 7.5 interplate earthquake. Our main objective is to highlight the major factors related to earthquake source that can bring the highest variability of ground motion at four broadband seismic stations across Mar tinique. For this purpose, we generated 320 rupture scenarios through a fractal kinematic source model, by varying rupture directivity, source dimension, slip distribution. We com puted the broadband ground motion (0.5-25 Hz) by convolution of source-time functions with Empirical Green’s Functions (EGFs), that we selected from the analysis of moderate events (M 4-4.5) recorded in the area of interest since 2016 by the West Indies network. We found that the fault geometry and the spatial extension of the largest slip patch are the most determinant source-related factors of ground motion variability. The significance of such ground motion variability with respect to ground motion prediction equations (GMPEs) depends on the evaluated frequency of ground motion and on the station. Moreover, we concluded that the EGF selection can be another significant factor of the variability of the modelled ground motion depending on station. Our results provide a new insight on the source-related ground-motion variability across Martinique and can guide future blind seismic hazard assessment studies in different regions.