Analysis of the 2014 (Mw 8.2) Pisagua Earthquake Sequence from Seismological and Geodetic Observations

The Pisagua (Mw 8.2) 2014 earthquake occurs within the central portion of the seismic gap defined by the great 1877 (Mw 8.8) earthquake, that took place at the Nazca-South American plate interface in Northern Chile. In 2007, the Tocopilla (Mw 7.7) earthquake has been the only other event occurring in the 1877 seismic gap, rupturing the southern and deepest portion of the megathrust. Both events account only for a small fraction of the slip deficit potentially accumulated in the region since 1877, thus not significantly reducing concerns for continued earthquake hazard. The April 1st, 2014 Pisagua earthquake was preceded by approximately two weeks of intense seismic activity that migrated to the mainshock hypocenter. A moderate Mw 6.7 shallow intraplate earthquake took place in March 16, 2014, triggering the whole seismic sequence. We aim to better understand the mechanical behavior of the subduction megathrust in the region affected by the Pisagua earthquake, from the modeling of the earthquake source. Here we analyze seismic source estimates for the Pisagua (Mw 8.2) 2014 event and its largest (Mw 7.7) aftershock constrained by geodetic and seismological observations. Preliminary models show the rupture process of the mainshock is characterized by a source duration of 80 s and a rather compact slip patch. Also modeling shows that rupture region of both events are located within regions of high coupling at the megathrust, surrounded by nearby regions that have been inferred to be prone to behave aseismically. We compare our results with the seismicity of the region, coupling models and megathrust regions inferred to have experienced aseismic slip behavior. We analyze the implications of our modeling in the context of the tectonics of the region and to the continuity of the seismic hazard in the region.