Local seismicity observed by a temporal network in the Villarrica-Valdivia region, South-Central Chile

DZIERMA, Y.; THORWART, M.; SIEGMUND, C.; RABBEL, W.; COMTE, D.; BATAILLE, K.; IGLESIA LLANOS, MARÍA P.; PREZZI, CLAUDIA BEATRIZ

San Francisco

Congreso; American Geophysical Union 2010 Fall Meeting; 2010

Understanding the processes behind subduction-related hazards is an important responsibility and major challenge for Earth scientists. Few areas demonstrate this as clearly as south-central Chile, where the largest instrumentally-recorded earthquake occurred (the 1960 Mw 9.5 Valdivia earthquake) in the same region as one of South America´s most active volcanoes, Villarrica. The geometry and geophysical characteristics of the subduction system are well constrained north of 39°S, but not further south where the 1960 coseismic slip was greatest. This region has long been considered a seismic gap due to the scarcity of local earthquakes registered in this region both by international networks (IRIS-NEIC) and the Chilean National Seismological Service (SSN). In the framework of the collaborative research centre SFB 574, the south-central Chilean subduction zone is investigated by a seismological subproject conducted by Chilean, Argentinian and German partners. This study presents results from a seismicity study based on a temporal local network of 55 stations between 39° and 40°S, covering the area from the coast to the back-arc in Argentina. The network was installed in November 2008 and ran for one full year, consisting of 40 short-period seismometers and 15 broad-band stations. The registered seismicity was significantly higher than expected, with more than 1000 observed events out of which about 300 earthquakes were localized in the area covered by the network. The plate interface where the 1960 slip occurred is free of seismicity. At greater depths, the Wadati-Benioff-Zone can be clearly observed down to depths of about 160 km with a dip angle of about 30°; some indication for a double Benioff-zone at shallower depths (ca. 60 km) is also found. In the continental crust, seismicity is observed related to local fault structures and the active volcanoes. Some clusters of seismicity are located offshore, possibly delineating fault structures in the incoming oceanic plate. In the vicinity of the trench, a large number of events is recorded, and focal mechanisms will be presented.