Near‐source velocity structure and isotropic moment tensors: A case study of the Long Valley Caldera

Abstract

The effect of near‐source velocity structure on the recovery of the isotropic component in moment tensor inversions is explored using a finite‐difference method. Synthetic data generated using a 3D Long Valley Caldera (LVC) velocity model (Vp +/− 20%) were inverted for the full moment tensor using a linear time‐domain scheme utilizing Green's functions calculated from 1D models. While inversions of synthetic data with input isotropic components recovered isotropic components with 95% significance according to an F‐test relative to deviatoric inversions (isotropic component constrained to zero), inversions of synthetic data with no input isotropic component recovered only nominal isotropic components with less than 75% significance. This study demonstrates near‐source structure does not appear to falsely produce significant isotropic components of moment tensor inversions in the passband typically employed by regional inversion methods.