Finite Element Models of Crustal Deformation and Stress Changes for Long Valley caldera and Mammoth Mountain volcano (California)

Seismic swarms, significant uplift centered at the resurgent dome and carbon dioxide emissions along the flanks of Mammoth Mountain volcano characterize the geological unrest at Long Valley caldera. Several authors suggest the presence of an inflating magmatic source beneath the caldera resurgent dome to explain the unrest. We use the Finite Element Method (FEM) to create an axial-symmetric model of the surface deformation due to a pressurization of a spheroidal source at depth. A big advantage of the FEM, when compared with analytical solutions, is the possibility to take into account mechanical and structural heterogeneities of the crust. A local model of the variation of seismic velocities with depth is used to infer elastic properties of the crust through empirical relations. We found that topography and crustal heterogeneities may have a significant influence (around than 10% of the signal) on surface deformation. Our results are compared with leveling, EDM and InSAR measurements from 1992 to 1999. We obtained a best fit with data for ΔP/µ=0.004, where ΔP is the excess pressure and µ the shear modulus. Finally we evaluate the distribution of stress to study the propagation of dykes beneath the resurgent dome and the influence that stress changes might have on the CO2 reservoir beneath Mammoth Mountain.