THE EFFECTS OF TOPOGRAPHY ON MAGMA CHAMBER DEFORMATION MODELS - APPLICATION TO MT-ETNA AND RADAR INTERFEROMETRY

We have used a three-dimensional elastic finite element model to exami ne the effects of topography on the surface deformation predicted by m odels of magma chamber deflation. We used the topography of Mt. Etna t o control the geometry of our model, and compared the finite element r esults to those predicted by an analytical solution for a pressurized sphere in an elastic half-space. Topography has a significant effect o n the predicted surface deformation for both displacement: profiles an d synthetic interferograms. Not only are the predicted displacement ma gnitudes significantly different, but also the map-view patterns of di splacement. It is possible to match the predicted displacement magnitu des fairly well by adjusting the elevation of a reference surface; how ever, the horizontal pattern of deformation is still significantly dif ferent. Thus, inversions based on constant-elevation reference surface s may not properly estimate the horizontal position of a magma chamber . We have investigated an approach where the elevation of the referenc e surface varies for each computation point, corresponding to topograp hy. For vertical displacements and tilts this method provides a good f it to the finite element results, and thus may form the basis for an i nversion scheme. For radial displacements, a constant reference elevat ion provides a better fit to the numerical results.