Finite-source attributes of 39 M 3.9 to 5.5 Ridgecrest, California earthquakes

Haoran Meng, Wenyuan Fan, Jeff J. McGuire, & Elizabeth S. Cochran

Published August 11, 2021, SCEC Contribution #11250, 2021 SCEC Annual Meeting Poster #191 (PDF)

We apply a time-domain approach that makes minimal assumptions to estimate the second-degree seismic moments of 39 M 3.9 to 5.5 earthquakes of the 2019 Ridgecrest, California sequence. Resolving earthquake rupture processes is essential both for understanding earthquake physics and for determining seismic hazards. However, it remains challenging to directly estimate the finite-source attributes of moderate and small earthquakes. Rupture processes of these events are traditionally resolved using spectral methods in the frequency domain. The second moments method, however, can characterize earthquake rupture length, width, duration, velocity, and directivity. We also quantify the finite-source model uncertainties by examining both model assumptions and data measurement uncertainties. These evaluations show that our second moments method can robustly resolve the earthquake source parameters. The resolved finite-source attributes suggest that most of these earthquakes ruptured bilaterally with a median rupture-speed of 69% of the local shear-wave speed. On average, the rupture length is 3.0 times the rupture width, deviating away from a circular crack. With the kinematic attributes, we compute the earthquake static stress-drops and obtained a median stress-drop estimate of 35.2 MPa using an elliptical crack model. The value is higher than that obtained from spectral analyses for earthquakes in the same region that assumes a circular rupture. Our stress-drop estimates indicate that these earthquakes, located around the M 7.1 mainshock and the M 6.4 foreshock, likely released a large portion of the total accumulated shear stress on their fault patches.

Key Words
finite-source attributes, second seismic moments, Ridgecrest earthquakes

Citation
Meng, H., Fan, W., McGuire, J. J., & Cochran, E. S. (2021, 08). Finite-source attributes of 39 M 3.9 to 5.5 Ridgecrest, California earthquakes. Poster Presentation at 2021 SCEC Annual Meeting.

Related Projects & Working Groups
Seismology