Stress state assessment through focal mechanism inversion in the San Salvador Metropolitan Area and its volcanic edifices, El Salvador

The San Salvador Metropolitan Area (SSMA) is the most populated urban nucleus of El Salvador, with a history marked by earthquakes. To date, only large-scale studies have described in general terms the state of stress and strain in the SSMA and the surrounding region. This work seeks to improve the level of detail, taking into account the geological structures present, the San Salvador volcano (SSV), and the Ilopango caldera (IC). Here we show maps of tectonic stress and strain obtained from the inversion of focal mechanisms and a 2D horizontal velocity field. The main results indicate that the strike-slip stress regime is responsible for generating the mainly transcurrent faults that cause destructive earthquakes in the Metropolitan Area, where the regional stress tensor governs, with a NW-SE σ 1 and a NE-SW σ 3 . The volcanic edifices show a stress rotation probably associated with magmatic bodies. As regards the strain in the study area seems to respond mainly to regional stress, presenting N E -SW extension axes, NW-SE shortening axes, and right lateral shear axes with E-W direction, but suggests a local strain for the SSV. The above findings provide information on the tectonic framework in which the seismic sequences are developed, important for future tectonic studies, seismic hazard assessment, and urban planning.