The recent seismic activity registered in the metropolitan areas of San Salvador (El Salvador) and Managua (Nicaragua) was analyzed to assess the seismic hazard and related risk scenarios. The affected areas lie along two main structural elements: the El Salvador Fault Zone (ESFZ), a segmented strike-slip fault zone with a E-W-trend, and the Nicaraguan Depression, a closely spaced system of NE-SW-trending strike-slip and oblique-normal faults. Focal mechanisms of shallow-crustal seismicity indicate strike-slip motion consistent with either left-lateral N/NE-oriented or, alternatively, right-lateral NW-oriented fault systems. The seismic activity (389 events) registered in the metropolitan area of San Salvador (April 9-11, 2017), Mmax 5.1, occurred in the Graben Central, a 30 km wide, E-W trending fault zone. Here historical seismicity indicated a near-surface, left-lateral N25°E-trending fault, located directly beneath the city of San Salvador (e.g. 6.7Mw event in 1917, 5.7Mw in 1986-1987). For the April 2017 swarm, preliminary results indicate a NNW-trending near-surface, left-lateral focal mechanism located in the Crustal zone that could be associated to a conjugate fault of the ESFZ or alternatively to the E-W right-lateral master faults. From March 28 to April 14, 2014, the metropolitan area of Managua was affected by a NW-SE-oriented seismic sequence (400 events) with 5.1-6.6 ML, and NW-SE compressional to alternatively NW-SE-right-lateral or NE-SW-left-lateral strike-slip focal mechanisms. The hypocentral depth ranges from 10 to 135 km. This seismicity developed in the Managua Graben where two catastrophic earthquakes occurred in the 20th century. We interpreted the 2014 swarm as due to a first deep event (65-135 km), located in the Subduction-Interface to Subduction-In-Slab zones, which reactivated a subsequent shallow sequence (10-15 km), located in the Crustal zone, according to the NW-SE-right-lateral system linked to the Lake Nicaragua-Lake Managua-Gulf of Fonseca pull-apart system, or alternatively to the NE-SW-left-lateral asymmetric system, conjugate with the NW-SE-master faults.
INTRAPLATE EARTHQUAKES IN CENTRAL AMERICA: RECENT SEISMIC ACTIVITY ANALYSIS IN EL SALVADOR AND NICARAGUA (RIESCA Project)
Esposito E;
2017
Abstract
The recent seismic activity registered in the metropolitan areas of San Salvador (El Salvador) and Managua (Nicaragua) was analyzed to assess the seismic hazard and related risk scenarios. The affected areas lie along two main structural elements: the El Salvador Fault Zone (ESFZ), a segmented strike-slip fault zone with a E-W-trend, and the Nicaraguan Depression, a closely spaced system of NE-SW-trending strike-slip and oblique-normal faults. Focal mechanisms of shallow-crustal seismicity indicate strike-slip motion consistent with either left-lateral N/NE-oriented or, alternatively, right-lateral NW-oriented fault systems. The seismic activity (389 events) registered in the metropolitan area of San Salvador (April 9-11, 2017), Mmax 5.1, occurred in the Graben Central, a 30 km wide, E-W trending fault zone. Here historical seismicity indicated a near-surface, left-lateral N25°E-trending fault, located directly beneath the city of San Salvador (e.g. 6.7Mw event in 1917, 5.7Mw in 1986-1987). For the April 2017 swarm, preliminary results indicate a NNW-trending near-surface, left-lateral focal mechanism located in the Crustal zone that could be associated to a conjugate fault of the ESFZ or alternatively to the E-W right-lateral master faults. From March 28 to April 14, 2014, the metropolitan area of Managua was affected by a NW-SE-oriented seismic sequence (400 events) with 5.1-6.6 ML, and NW-SE compressional to alternatively NW-SE-right-lateral or NE-SW-left-lateral strike-slip focal mechanisms. The hypocentral depth ranges from 10 to 135 km. This seismicity developed in the Managua Graben where two catastrophic earthquakes occurred in the 20th century. We interpreted the 2014 swarm as due to a first deep event (65-135 km), located in the Subduction-Interface to Subduction-In-Slab zones, which reactivated a subsequent shallow sequence (10-15 km), located in the Crustal zone, according to the NW-SE-right-lateral system linked to the Lake Nicaragua-Lake Managua-Gulf of Fonseca pull-apart system, or alternatively to the NE-SW-left-lateral asymmetric system, conjugate with the NW-SE-master faults.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
