Seismological investigations around Villarrica Volcano, Southern Chile – First Results

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

Freudenstadt

Congreso; 35. Sitzung der AG Seismologie.; 2009

In addition to presenting a continental end-member of subduction zones, seismicity and volcanism in the Chilean subduction zone are influenced strongly by sediment input into the trench, oblique convergence and strain partitioning, and pre-Andean characteristics of the overriding plate. Furthermore, the occurrence of the largest instrumentally recorded earthquake, the Valdivia 1960 earthquake, close to the very active Villarrica volcano, makes this region ideally suited for subduction-related hazard investigations. As a part of the SFB 574 “Volatiles and Fluids in Subduction Zones“, network of 55 seismological stations was installed in November 2008 between 39 deg and 40 deg South. The stations are distributed from the coast to the back-arc in Argentina, linking the volcano Villarrica with the area of maximum coseismic slip of the 1960 Valdivia earthquake. In April 2009, three additional stations were deployed on the flanks of Villarrica and Quetrupillan. Data recording will continue until October 2009. The data collected by this network will serve for seismicity, local and teleseismic tomography, receiver function and anisotropy studies. This poster presents a data example and first results from the ongoing seismicity study. Two months of data recording have been picked and preliminarily localized so far. In that time 25 events were recorded inside the area covered by the network, rising to 77 events if the vicinity of the network is considered (100 km to either side). Although this region has been considered a seismic gap due to the scarcity of seismicity in comparison with adjacent segements along the Chilean subduction zone, the Wadati-Benioff-Zone is clearly traced by the events down to about 140 km depth, at an angle of about 35°. In addition to exploring the deep structure and geometry of the subduction zone, ongoing and future studies are expected to provide insight into the presence of fluids, fluid pathways, and the stress field. In combination with geochemical and volcanological studies also performed by the SFB 574, these investigations will contribute to a better understanding of subduction zone characteristics in a region of extreme coseismic stress, slab-arc fluid processes, volcano dynamics and hazards.