Finite-source attributes of 39 M3.8 to M5.5 Ridgecrest earthquakes

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

In Preparation March 14, 2021, SCEC Contribution #10958

Resolving earthquake rupture processes is essential for understanding earthquake physics and mitigating seismic hazards. However, it remains challenging to directly solve the finite-source attributes for moderate and small earthquakes, and rupture processes of such events are traditionally resolved using spectral methods in the frequency domain based on pre-assumed rupture models. In this study, we apply a time-domain approach that makes few assumptions to estimate the second-degree seismic moments of 39 M3.8 to 5.5 earthquakes of the 2019 Ridgecrest sequence. The 39 earthquakes occurred on faults that are both parallel and perpendicular to the strike of the Mw~7.1 mainshock. The second moments can represent earthquake finite-source attributes, including the rupture length, width, duration, and directivity. We also quantify the model uncertainties by perturbing the earthquake depth, rotating focal mechanism, and jackknife-resampling the stations. These tests show that our second moments method can robustly resolve the earthquake source parameters. Our models suggest that most of these earthquakes ruptured bilaterally with a median rupture-speed of 74% of the local shear-wave speed. On average, the rupture length is 3.6 times longer than the rupture width, and the earthquake duration seems to scale with its magnitude. With the kinematic attributes, we estimate the earthquake stress-drops and obtained a median stress-drop of 47 MPa. The value is higher than that obtained from spectral analyses. Our stress-drop estimates indicate that these earthquakes likely released a large portion of the total accumulated shear stress of the fault patches.

Meng, H., Fan, W., McGuire, J. J., & Cochran, E. S. (2021). Finite-source attributes of 39 M3.8 to M5.5 Ridgecrest earthquakes. Journal of Geophysical Research: Solid Earth, (in preparation).