Rapid after shock deployment after the Mw=6.2 Aysen earthquake in Southern Chile

Abstract

On February 23rd 2007, an earthquake M=5.2 took place in the Aysen Fjord, Southern Chile and started a sequence of earthquakes that culminated, at least in its critical phase, with the M=6.2 Aysen earthquake. The Aysen earthquake not only caused damage to buildings and installation, but also a significant number of casualties were reported. The aim of this study focuses on analysing the aftershock sequence of the main event in order to characterize the seismo-tectonics of this zone, which was formerly believed to have no significant seismic hazard. Up to now we determined accurate event locations by simultaneously inverting for station corrections and a 1D velocity structure. We also calculated preliminary fault plane solutions based on first motion polarities. The results show that the aftershock seismicity is related to the main structure present in the area, the Liquiñe-Ofqui Fault Zone (LOFZ) and it is generated at shallow depths. Furthermore, fault plane solutions for some of the events indicate right strike slip faulting NNE trending which also coincides with the geometry and nature of this intra-arc transcurrent fault. Additionally, a new alignment of seismic events trending ENE has been observed in the region, which could be interpreted as a reactivation of an old structure or the rupture and development of a completely new fault subordinate to the main fault.