DEFORMATION-INDUCED GRAVITY CHANGES IN VOLCANIC REGIONS

We analyse a new model to estimate the change in gravity and in elevation caused by volcanic eruption or inflation. In the new model, a permeable, porous zone surrounds a spherical magma chamber. Magma may enter or leave the magma chamber and, independently, the permeable zone. This arrangement simulates the flow processes inferred from field studies, and provides a degree of freedom not available in the classic model proposed by Mogi and used by many others since then. We find, in agreement with field data and previous analyses of the Mogi model, that the change in edifice volume is smaller than the volume of magma which produces it. The local change in gravity is found to be proportional to the local elevation change, the constant of proportionality being positive or negative, depending on whether magma flow is directed into or out of the chamber or infiltrated zone.