Isotropic Source Components of Events in the 2019 Ridgecrest, California, Earthquake Sequence

We investigate the non-double-couple components of 224 M ≥ 3.0 earthquakes in the 2019 M_w7.1 Ridgecrest sequence, which occurred on a complex fault system in the Eastern California Shear Zone. Full moment tensors are derived using waveform data from near-fault and regional stations with a generalized cut-and-paste inversion and 3-D velocity and attenuation models. The results show limited Compensated Linear Vector Dipole components, but considerable explosive isotropic components (5%–15% of the total moments) for approximately 50 earthquakes. Most of these events occur between the M_w6.4 foreshock and 1 day after the M_w7.1 mainshock and are mainly distributed around the rupture ends and fault intersections. The percentage of isotropic components is reduced considerably when data recorded by near-fault stations are not included in the inversions, highlighting the importance of near-fault data. The results suggest that high-frequency damage-related radiation and other local dilatational processes are responsible for the observed isotropic source terms.