Seismologic link between the subducted Valdivia fault zone and Villarrica volcano, Chile

The subduction of the Nazca plate caused two of the largest earthquakes (1960 Mw 9.5 Valdivia and 2010 Mw 8.8 Maule) in the last 100 years. Major fault zones of the Nazca Plate like the Valdivia fault zone and the Mocha fault zone seem to behave as a barrier for the rupture propagation. Villarrica volcano is in the region of the maximum slip of the 1960 Mw 9.5 earthquake and is one of South America's most active volcanoes. This part of the south-central Chilean subduction zone was investigated by a seismological experiment within the framework of the collaborative research center SFB 574. In the extension of the Valdiva fault zone we observed increased seismicity in the subducting plate at depths between 80 km and 120 km, where dehydration of the subducting plate occurs. Tomographic images show decreased P- and S-velocity and increased ratio between this cluster and the volcanic center of Villarrica, Quetrupillán and Lanin, indicating a increased content of fluids. Additionally, magma of Villarrica volcano shows a strong fluid signal in geochemical measurements. We think that the Valdivia fault zone serves as the source for the fluids. Before the plate subducts, water can penetrate the plate through faults with in the Valdivia fault zone. Serpentinization would build the water into minerals. Inside the subduction zone the Valdiva fault zone is reactivated by dehydration reactions at a depth of about 100 km. The released fluids rise towards the volcanic center causing the tomographic anamolies. At the end this leads to an increased degree of melting and a higher activity of Villarrica volcano.