SCEC Award Number 20115 View PDF
Proposal Category Individual Proposal (Data Gathering and Products)
Proposal Title Resolving Finite Source Attributes of Moderate Magnitude Earthquakes of the 2019 Ridgecrest Earthquake Sequence
Name Organization
Haoran Meng Florida State University Wenyuan Fan Florida State University
Other Participants N/A
SCEC Priorities 1d, 2d, 4a SCEC Groups Seismology, FARM, SDOT
Report Due Date 03/15/2021 Date Report Submitted 03/15/2021
Project Abstract
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.
Intellectual Merit This project directly solves finite source attributes of moderate to small earthquakes and advances our understanding of their rupture processes. It also offers a quantitative framework to investigate the source attribute uncertainties and advances our understanding of the variabilities of earthquakes in a single fault system. Finally, our results show that the Ridgecrest earthquakes likely released a large portion of the total shear stress that was accumulated at the fault patches.
Broader Impacts The project contributed to the training of a postdoctoral scholar, Haoran Meng. Haoran was supported to participate in the 2020 SCEC meeting and to engage with the SCEC community. A research article detailing our results is currently under preparation. All the data-product will be made publicly available upon publication. We work closely with the proposed stress-drop validation TAG and share and integrate our research efforts as part of the larger community endeavor of studying earthquake source parameters.
Exemplary Figure Caption of Figure 4: Finite source attributes of 39 M3.8 to M5.5 Ridgecrest earthquakes. (a), characteristic durations of earthquakes along profile AA’ showing in Figure 1. Earthquake magnitude scales with the circle size. The grey and light blue contours show the slip distribution of the Mw 7.1 mainshock and the Mw 6.4 foreshock of the 2019 Ridgecrest earthquake sequence, respectively (Jia et al., 2020). (b-d), ratio of the scaled rupture velocity and the local shear velocity (b), directivity ratio (c), and stress drop estimates (d) for earthquakes along profile AA’. (e-h) similar to (a-d) but along profile BB’ (Figure 1).