Tectonic setting of the northwestern andes Constrained by a high-resolution earthquake catalog: Block Kinematics

Abstract

A high-precision earthquake catalog was generated using source-specific station terms and waveform cross-correlation techniques. This detailed catalog serves to interpret the crustal structure and deformation related to the tectonic setting in Northwestern South America. The Panamá-Chocó Block (PCB) is in contact with the Northwestern Andes causing crustal deformation and hence, fault interaction in the brittle regime leading to a high earthquake production concentrated in the Murindó Seismic Cluster (MSC) which is located in the northeastern corner of the PCB. Slip on the Uramita Fault Zone (UFZ) is a response to the accommodation of the PCB against the North Andean block (NAB), splitting the fault into two segments, marked by an abrupt change in its strike. The north segment of the UFZ, a dextral transform fault (strike = S52°E and near vertical plane), which produced the Mutatá earthquake (2016-09-14, Mw = 6.2). The central segment of the UFZ strikes N12°E and exhibits mainly reverse slip with a subvertical fault plane which produced the 1987-03-19 Mw = 5.4 and 1987-11-11 Mw = 5.3 events. The Murindó sinistral strike-slip fault (strike = N9°W), which produced the great Murindó earthquake (1992-10-18, Mw = 7.1, epicentral intensity XI) is characterized by its wide zone of brittle deformation as a response to internal deformation of the PCB under a compressional NW-SE stress. Intermediate depth earthquakes are widely observed in the area, where we find evidence of the Caribbean slab subducting southwards beneath Panamá. The subduction of the Malpelo microplate to the south, shows high productivity within the Cauca Cluster and the presence of at least three finger-shaped mantle zones of seismicity.