Open AccessSeismo‐tectonic structure of the Aysén Region, Southern Chile, inferred from the 2007 M w = 6.2 Aysén earthquake sequence
Author(s) -
Agurto H.,
Rietbrock A.,
Barrientos S.,
Bataille K.,
Legrand D.
Publication year - 2012
Publication title -
geophysical journal international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.302
H-Index - 168
eISSN - 1365-246X
pISSN - 0956-540X
DOI - 10.1111/j.1365-246x.2012.05507.x
Subject(s) - seismology , geology , aftershock , induced seismicity , foreshock , tectonics , crust , fault (geology) , sequence (biology) , focal mechanism , geodesy , geophysics , biology , genetics
SUMMARY On 2007 April 21, a M w = 6.2 earthquake shook the Aysén Fjord, Southern Chile in an unprecedented episode for this region characterized by low seismicity. The area is intersected by the Liquiñe‐Ofqui Fault System (LOFS), a +1000‐km‐long strike‐slip fault that absorbs part of the oblique convergence motion between Nazca and South America plates. To study the aftershock sequence of this main event, we installed a seismic network of 15 stations in the area for a period of nearly 7 months. We characterized the seismogenic structure of the zone by calculating a minimum 1‐D local velocity model and obtaining precise hypocentral coordinates and uncertainty estimates by using a non‐linear probabilistic approach. We also obtained fault plane solutions based on first motion polarities and SV / P amplitude ratios. The velocity model shows an average V p / V s ratio of 1.76 for the area and low shear wave velocity values for the upper 3 km of crust. The aftershock seismicity was located mainly between 4 and 10 km depth and disposed in (1) an ∼N–S trending alignment that follows the trace of the LOFS and (2) an E–W alignment at the East of the main fault. Furthermore, we re‐analysed the previously published foreshock and early aftershock activity of the sequence including four of its largest events, improving considerably previous location estimates. Selected focal mechanisms show a strong strike‐slip component that coincides with the nature of the LOFS. Based on our new analysis we conclude that the 2007 Aysén seismic sequence had a tectonic origin related to activity on the southern end of the LOFS, however not discarding the presence and potential action of fluids on the aftershock activity.