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

The effect of near-source velocity structure on the recovery of the isotrop ic component in moment tenser inversions is explored using a finite-differe nce method. Synthetic data generated using a 3D Long Valley Caldera (LVC) v elocity model(V-p +/- 20%) were inverted for the full moment tenser using a linear time-domain scheme utilizing Green's functions calculated from 1D m odels. While inversions of synthetic data with input isotropic components r ecovered 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 stu dy demonstrates near-source structure does not appear to falsely produce si gnificant isotropic components of moment tensor inversions in the passband typically employed by regional. inversion methods.