Rapid deployment of a seismic network to record the aftershocks of the Mw=6.2 Aisen earthquake in Southern Chile

The largest earthquakes (e.g. Chile, 1960; Andaman-Sumatra, 2004) are generated at convergent plate boundaries, where oceanic plates subduct beneath other tectonic plates. During plate convergent, large stresses build up causing major earthquakes. Understanding the stress distribution would foster our knowledge of earthquake occurrence and might lead to better prediction of maximum possible magnitudes in the future at given segments of a subduction zone. However, a detailed knowledge of the coupling forces and the stress distribution in the overriding plate is still lacking, especially in the case of oblique subduction in which bulk transpressional deformation is expected. Precise earthquake locations together with fault plane solutions provide important constraints to solve this problem. The Aisen Southern Chile earthquake at 45.4 S on April 21, 2007 gives a unique possibility to study the stress distribution since it occurred in an ideal natural laboratory. Different segments of the Southern Chilean margin have been studied recently (2004/2005) by several temporal seismic networks also incorporating the rupture area of the 1960 Chile earthquake (Rietbrock et al, 2004; Haberland et al., 2006; Lange et al., 2007). However, due to the low seismicity of the Aisen region, this important segment, where the rupture of the 1960 earthquake ended, could not be studied so far. Using the current aftershock activity this can be rectified; it may be the only chance for such a study in the foreseeable future.