Volcanic seismology studies at Copahue volcano- Argentina

BENGOA C L, CASELLI, A T Y J M. IBÁÑEZ

Tenerife

Congreso; Cities on Volcanoes 6; 2010

ITER

Seismic activity registered from seismic field survey carried out at Copahue volcano, Southern Andes, Argentina, using a small-aperture, dense seismic arrays. Copahue volcano (37º45‘S; 71º10.2ºW, 2965 m) is located in the border Argentina-Chile, in the extreme southwest of the Caviahue caldera (Caviahue-Copahue complex- southern Andean Volcanic Zone). It has numerous historical eruptions, where his last and most important activity took place in July 2000. Caviahue-Copahue complex is characterized mainly by emissions andesitic and basaltic andesitic and it is located in the transition zone between two major fault systems, Liquiñe Ofqui fault zone and Copahue–Antiñir thrust system. Volcano seismology studies are important to understand different aspects of the volcanic system. An analysis of the data recorded between November 2003 and January 2010 from the different seismic arrays has been able to identify high-frequency events such as volcano-tectonic earthquakes (VT) and long period events (tremor). Local VT events were identified (difference in arrival times of phase waves between P and S less than 10 sec.) generally, these events display clear P and S wave arrivals, high-frequencies spectral content, between 1 and 16 Hz and they are related to brittle fractures. They have been located in two areas, one near Caviahue village (about 9 km east of the volcano) possibly related to an existing horst-graben system inside the caldera. These events are characterized by having VT epicentral distances less than 32 km and 15 km depth according to the seismic array located near to Caviahue village; and another one, in the area of the Barco lake (southwest of the volcano-Chilean territory). Long period events expose spectral energies usually concentrated at frequencies of 1 and 2 Hz and array solutions show a predominant slowness vector pointing to geothermal fields located about 6 km north of the array site.