Finite-source attributes of 39 M 3.9 to 5.5 Ridgecrest, California earthquakes
Haoran Meng
University of California, San Diego
- Date & Time
- Location
- Online-only seminar via Microsoft Teams
- Host
- Jeffrey McGuire
- Summary
Resolving earthquake rupture processes is essential for understanding earthquake physics and determining seismic hazards. However, it remains challenging to directly solve the finite-source attributes of moderate and small earthquakes; rupture processes of such events are traditionally resolved using spectral methods in the frequency domain. In this study, 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 from the 2019 Ridgecrest, California sequence. The second moments can characterize earthquake finite-source attributes, including the rupture length, width, duration, velocity, and directivity. We also quantify the finite-source model uncertainties by examining both model assumptions and data imperfections. These evaluations show that our second moments method can robustly resolve the earthquake rupture length and duration. The rupture width, velocity, and directivity ratio may suffer uncertainties when the network configuration is less optimal. The resolved finite-source attributes of the 39 earthquakes show no clear spatial patterns. Most of these earthquakes ruptured bilaterally with a median scaled 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-drop and obtained a median stress-drop estimate of 35.2 MPa with a median lower bound of 1.8 MPa assuming an elliptical crack model. We show that model assumptions can lead to up to two orders of magnitude differences in the stress-drop estimates for the same earthquakes with the same set of measurements.
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