We have investigated the effects of the topography on the surface deformation and gravity changes caused by a magmatic infrusion in the Earth's crust. Considering axisymmetrical volcanoes and the varying depth methodology we show that topography has significant effecf on the magnitude of the predicted displacements and gravity changes. We see the reducfion of the magnitude close to the summit of the volcano. The topography effect is emphasized if we introduce the mass of the intrusion jointly with the dilation/compression of the magma chamber due to pressure change. Using the elastic-gravitational model introduced by Rundle (1980) that considers the interaciion of the intrusion mass with the ambient gravity field we show that neglecting the topographic effects may, in some cases, introduce an error greater than neglecting the ambient gravity field. We apply the described methodology to Mayon volcano, Philippines, to compute the gravity changes caused by an intrusion located in an elastic-gravitational halfspace. It can be seen that inversions based on spherical magma chamber model could gain accuracy by using varying elevation analytical solution. We show that, for inversions based on observed gravity changes, the amount of pressure or mass increment would be significantly underestimated and the depth of the chamber could be overestimated ifthe topography is not considered.

Comunicación presntada a la 3ª Asamblea Hispano-Portuguesa de Geodesia y Geofísica = 3ª Assembleia Luso-Espanhola de Geodesia e Geofisica, celebrada en Valencia entre el 4 y el 8 de febrero de 2002.

Peer reviewed