Attenuation Tomography of Sierra Negra Volcano of the Galapagos Archipelago

Abstract:

Following relocation of events with the double-difference location algorithm (HypoDD), we apply tomographic methods to extract 3D attenuation models illuminating the plumbing system of the Sierra Negra Caldera of the Galapagos Archipelago. The dataset consists of 1737 events recorded from July 2009 to June 2011 on the 17-station SIGNET broadband seismic array. We use t* spectral decay methods for both P- and S- phases with the clustered locations to highlight locations where significant variations in Q suggest the presence of magma melt. While the presence of a magma sill, at least 2 km depth, is indicated by InSAR and GPS studies, the delineated magma body has not been explored in detail. The lower bound of the proposed magma accumulation is still under question and thus forms the primary target of this research. Melt replenishment and degassing of the magma sill is believed to cause inflation and/or deflation of the caldera floor. Imaging the extent of the magma sill will provide insight into the feeder system and deformation process of the Sierra Negra caldera. Detailed relocation, Qp and Qs inversion, as well as estimates of the scattering attenuation using coda-normalization technique will be presented. The close relationship between seismic attenuation and the thermal state of the magmatic system suggests we can distinguish melt and/or fluid regions within the Sierra Negra plumbing system.