Future magnitude 7.5 earthquake offshore Martinique: spotlight on the main source features controlling ground motion prediction

The eastern offshore of Martinique is one of the active areas of the Lesser Antilles Subduction 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 M 8 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 how ground motion can vary for a hypothetical M-w 7.5 interplate earthquake. Our main objective is to highlight the major factors related to earthquake source that can cause the highest variation in ground motion at four broad-band seismic stations across Martinique. For this purpose, we generated 320 rupture scenarios through a fractal kinematic source model, by varying rupture directivity, source dimension, slip distribution. We computed the broad-band 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 influential factors on ground motion. The significance of the variation of the predicted ground motion 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 controlling the modelled ground motion depending on station. Our results provide a new insight for the seismic source impact on ground motion across Martinique and can guide future blind seismic hazard assessment studies in different regions.

Automated summary

The eastern offshore of Martinique is an active region of the Lesser Antilles Subduction Zone capable of generating strong earthquakes. Factors such as fault geometry and slip patch spatial extension were found to be influential in ground motion variation, with the selection of empirical Green's functions impacting the modelled ground motion. This study provides insights for seismic source impact on ground motion in Martinique and can guide future seismic hazard assessment studies.