The May 10, 1994 earthquake: evidence of a seismic preslip in the northern Chile seismic gap?

Abstract

The focal depth and the focal mechanism solution of the May 10, 1994 earthquake (mb=5.9) were 'obtained using the long period P, SV, and SH waveforms of stations located at teleseismic distances. Its epicenter was determined by a joint determination using arrival times of teleseismic and local networks. The focal mechanism obtained by the body waveform inversion corresponds to thrust faulting occurring at a depth of 58 km. On August 8, 1987, a tensional event (~=6.4) occurred with focal depth of 76 km. Both this event and the 1994 compressional event are located in the northern edge of the 1877 rupture area at a distance of about 200 km from the trench, close to the coupled-uncoupled transition of the subducting Nazca plate. A cluster of compressional events with magnitudes 5.0 ~mb~5.3 is also reported herein. This cluster, located· offshore and aligned with the 1994 earthquake in the direction of plate convergence, could be associated with one of the main asperities of the future great earthquake expected in northern Chile. The occurrence of the 1987 and 1994 earthquakes has been unusual given the last 32 years of available information, and suggests that they could be associated with seismic pre-slip occurring in the deeper part of the seismogenic interplate contact of the northern Chile seismic gap, which could be close to the end of its seismic cycle.