HR: 0800h
AN: V11B-1432    [Abstracts]
TI: SPATIAL AND TEMPORAL CHANGES OF CODA Q IN THE GALERAS VOLCANO, COLOMBIA
AU: * Vargas-Jim‚nez, C A
EM: cavargasj@unal.edu.co
AF: Posgrado de Geofˇsica, Departamento de Geociencias Universidad Nacional de Colombia Ciudad Universitaria, Bogota, D.C. Colombia
AU: Duran-Tovar, J P
AF: Posgrado de Geofˇsica, Departamento de Geociencias Universidad Nacional de Colombia Ciudad Universitaria, Bogota, D.C. Colombia
AU: Moncayo, E
AF: Posgrado de Geofˇsica, Departamento de Geociencias Universidad Nacional de Colombia Ciudad Universitaria, Bogota, D.C. Colombia
AU: Montes-Vidal, L A
AF: Posgrado de Geofˇsica, Departamento de Geociencias Universidad Nacional de Colombia Ciudad Universitaria, Bogota, D.C. Colombia
AU: Castillo-L˘pez, L A
AF: Posgrado de Geofˇsica, Departamento de Geociencias Universidad Nacional de Colombia Ciudad Universitaria, Bogota, D.C. Colombia
AU: Caneva-Rincon, A
AF: Centro de Investigaciones - Area de Geofˇsica - Universidad Antonio Nari¤o, Calle 59B No 37-71 oficina 201, Bogota, D.C. Colombia
AB: Spatial and temporal changes of coda Q was analyzed for the Galeras volcano, located in the Andes of southwestern Colombia. The $Q^{-1}$ value was calculated using the Single Backscattering (SBS) working with seismograms filtered in frequency bands centered in 1.5, 3.0, 6.0 and 12.0 Hz. The temporal variation analysis was done following the frequency dependence $Q=Qof^{-n}$ before and after some eruptions. The temporal change of attenuation has two stages, the first is the 1989-1992 period, when the $Q^{-1}$ value shows an increasing tendency. The other is the 1992-2002 period that is characterized for a decreasing in the $Q^{-1}$ value. The rise of attenuation before July 92 eruption is associated with an andesitic dome extrusion, after this eruption the dome is destroyed and the $Q^{-1}$ value falls. Since 1994 low attenuation values are associated with the low activity stage of Galeras until recently activity at 2004. The frecuencial dependence shows that the $Q^{-1}$ value rises before an eruption and falls after this. The results show a clear change of attenuation before and after the eruptions so that coda $Q^{-1}$ is a premonitory tool for this volcano and we suggest it to be used in the Galeras activity monitoring. On the other hand, we have extended the first scattered concept for the inversion of spatial values of coda-Q. Two important anomalies was found, the first one at 9 km depth which is related to the main magmatic camera where are occurring process that feed the second one at 4km depth. Other minor anomalies has been correlated with faults that crossing the volcano.
DE: 8419 Eruption monitoring (7280)
DE: 7280 Volcano seismology (8419)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting