Triggered seismicity in the Andean arc region via static stress variation by the MW=8.8, February 27, 2010, Maule earthquake

Abstract

We localized crustal earthquakes in the Andean arc, between 35°S and 36°S, from December 2009 to May 2010. This research shows a seismicity increase, in a narrow longitudinal area, of more than nine times after the great Mw 8.8 Maule earthquake. The localized seismicity defines an area of 80 km long and 18 km wide and NNW to NNE trend. The Md magnitudes varied from 0.7 to 3.1 except for two earthquakes with Mw of 3.9 and 4.5, located in the northern end of the area. The focal mechanisms for these two last events were normal/strike-slip and strike-slip respectively.During 2011, a network of 13 temporary stations was installed in the trasarc region in Malargüe, Argentina. Sixty earthquakes were localized in the study region during an 8 month period. We explored how changes in Coulomb conditions associated with the mega-thrust earthquake triggered subsequent upper-plate events in the arc region. We assumed the major proposed structures as receiver faults and used previously published earthquake source parameters and slip distribution for the Maule quake. The largest contribution to static stress change, up to 5 bars, derives from unclamping resulting consistent with co-seismic dilatational deformation inferred from GPS observations in the region and subsidence in nearby volcanoes caused by magma migration.Three different Quaternary tectonic settings; extensional, strike-slip and compressional- have been proposed for the arc region at these latitudes. We found that the unclamping produced by the Maule quake could temporarily change the local regime to normal/strike-slip, or at least it would favour the activation of Quaternary NNE to N-trending dextral strike-slip faults with dextral transtensional movement.