RECENT INTRAPLATE EARTHQUAKES IN CENTRAL AMERICA (MEXICO, EL SALVADOR, AND NICARAGUA IN THE FRAME OF THE SUBDUCTION GEOMETRY VARIABILITY

The seismic activity registered in the metropolitan areas of San Salvador (El Salvador), April 2017, with M 5.1, and Managua (Nicaragua), March-April 2014, with M 5.1-6.6, lies along two main NW-SE structural elements, affecting the Central America Volcanic Arc: the El Salvador Fault Zone, a segmented strike-slip fault zone with a dominant E-W-trend, and the Nicaraguan Depression, a system of NE-SW-trending strike-slip and oblique-normal faults. The San Salvador activity indicates a NNW-trending near-surface, left-lateral focal mechanism located in the Crustal seismogenic zone, associated to a conjugate fault of the El Salvador Fault Zone or alternatively to the E-W right-lateral master faults. The Managua activity was interpreted as due to a first deep event (65-135 km depth), located in the Subduction Interface to Subduction In-Slab seismogenic zones, which reactivated a subsequent shallow sequence (10-15 km depth), located in the Crustal seismogenic zone, according to the NW-SE right-lateral system, or alternatively to the conjugate NE-SW left-lateral asymmetric system. The recent seismic activity registered on 2017, September 7 (M 8.1) and 19 (M 7.1) offshore South-Western Mexico and in Central Mexico, was located along the Middle America Trench and in the Mexican volcanic arc respectively. Focal mechanisms indicate NW-SE-trending normal faulting consistent with extension in the subduction hinge of the Cocos plate, at intermediate depths (50-60 km). The recent and historical seismicity demonstrates that, independently form their magnitude, they are capable of producing severe damages because of their shallow depth.