Effects of crustal layering on the inversion of deformation and gravity data in volcanic areas: An application to the Campi Flegrei caldera, Italy

Abstract

We study the effects of crustal layering on ground displacements and gravity changes due to a spheroidal expanding source. Soft superficial layers affect the deformation pattern (giving an apparent shallower source if layering is not taken into account), the ratio of horizontal to vertical displacements (biasing the source shape), and the subsurface mass redistribution effects on gravity changes. Retrieved intrusion density is biased toward very low values if the source is modelled as a penny-shaped crack (point and finite) in a homogeneous half-space and the resulting density misestimate can lead to a possibly incorrect assessment of volcanic hazard. As an application, we consider the 1982-1984 Campi Flegrei unrest. We show that the large discrepancy between densities of spherical and penny-shaped sources, given in the literature and obtained inverting ground displacement and gravity data in a homogeneous half-space, is at least partially a consequence of the homogeneous half-space assumption. Copyright 2007 by the American Geophysical Union.