Overview of the SCEC/USGS Community Stress Drop Validation Study Using the 2019 Ridgecrest Earthquake Sequence

Creators: Abercrombie, Rachel E.¹; Baltay, Annemarie²; Chu, Shanna³; Taira, Taka'aki⁴; Bindi, Dino⁵; Boyd, Oliver S.⁶; Chen, Xiaowei⁷; Cochran, Elizabeth S.²; Devin, Emma⁸; Dreger, Douglas⁴; Ellsworth, William⁹; Fan, Wenyuan¹⁰; Harrington, Rebecca M.¹¹; Huang, Yihe¹²; Kemna, Kilian B.¹¹; Liu, Meichen¹³; Oth, Adrien¹⁴; Parker, Grace A.²; Pennington, Colin¹⁵; Picozzi, Matteo¹⁶; Ruhl, Christine J.¹⁷; Shearer, Peter¹⁰; Spallarossa, Daniele¹⁸; Trugman, Daniel¹⁹; Vandevert, Ian¹⁰; Wu, Qimin; Yoon, Clara²; Yu, Ellen¹³; Beroza, Gregory C.⁹; Eulenfeld, Tom²⁰; Knudson, Trey⁹; Mayeda, Kevin²¹; Morasca, Paola²²; Neely, James S.²³; Roman-Nieves, Jorge²¹; Satriano, Claudio²⁴; Supino, Mariano²²; Walter, William R.¹⁵; Archuleta, Ralph²⁵; Atkinson, Gail Marie²⁶; Calderoni, Giovanna²²; Ji, Chen²⁵; Yang, Hongfeng²⁷; Zhang, Jiewen²⁷

1. Boston University
2. United States Geological Survey
3. Rice University
4. University of California, Berkeley
5. Helmholtz Centre Potsdam - GFZ German Research Centre for Geosciences
6. U.S. Geological Survey, Geologic Hazards Science Center, Golden, Colorado, U.S.A.
7. Texas A&M University
8. Princeton University
9. Stanford University
10. University of California, San Diego
11. Ruhr University Bochum
12. University of Michigan–Ann Arbor
13. California Institute of Technology
14. European Center for Geodynamics and Seismology
15. Lawrence Livermore National Laboratory
16. National Institute of Oceanography and Experimental Geophysics
17. Verisk Analytics (United States)
18. University of Genoa
19. University of Nevada Reno
20. Friedrich Schiller University Jena
21. Air Force Technical Applications Center, Patrick Space Force Base, Florida, U.S.A.
22. National Institute of Geophysics and Volcanology
23. University of Chicago
24. Institut de Physique du Globe de Paris
25. University of California, Santa Barbara
26. Western University
27. Chinese University of Hong Kong

Abstract

We present initial findings from the ongoing Community Stress Drop Validation Study to compare spectral stress-drop estimates for earthquakes in the 2019 Ridgecrest, California, sequence. This study uses a unified dataset to independently estimate earthquake source parameters through various methods. Stress drop, which denotes the change in average shear stress along a fault during earthquake rupture, is a critical parameter in earthquake science, impacting ground motion, rupture simulation, and source physics. Spectral stress drop is commonly derived by fitting the amplitude-spectrum shape, but estimates can vary substantially across studies for individual earthquakes. Sponsored jointly by the U.S. Geological Survey and the Statewide (previously, Southern) California Earthquake Center our community study aims to elucidate sources of variability and uncertainty in earthquake spectral stress-drop estimates through quantitative comparison of submitted results from independent analyses. The dataset includes nearly 13,000 earthquakes ranging from M 1 to 7 during a two-week period of the 2019 Ridgecrest sequence, recorded within a 1° radius. In this article, we report on 56 unique submissions received from 20 different groups, detailing spectral corner frequencies (or source durations), moment magnitudes, and estimated spectral stress drops. Methods employed encompass spectral ratio analysis, spectral decomposition and inversion, finite-fault modeling, ground-motion-based approaches, and combined methods. Initial analysis reveals significant scatter across submitted spectral stress drops spanning over six orders of magnitude. However, we can identify between-method trends and offsets within the data to mitigate this variability. Averaging submissions for a prioritized subset of 56 events shows reduced variability of spectral stress drop, indicating overall consistency in recovered spectral stress-drop values.

Copyright and License

Acknowledgement

The authors and PIs of this research project are appreciative of all the global community support and enthusiasm for this collaborative work, and thank and acknowledge everyone who has participated in the various workshops and discussions. The authors also thank the editors and reviewers who handled this article, improving its quality, including T. Uchide and B. Enescu. This research was supported by Southern California Earthquake Center (SCEC) (Award Numbers 24067, 23107, 23108, 22034, 22042, 22101, 22027, 21032, 21045, 21083, 21114, and 21169, including salary support for T. Taira, D. Dreger, C. Ruhl, X. Chen, P. Shearer, X. Chen, Q. Wu, W. Ellsworth, T. Knudsen, and financial support for the 2022 September workshop). The authors are also grateful to T. Huynh and E. Pauk for their invaluable logistical support. R. Abercrombie is grateful for U.S. Geological Survey (USGS) support though an IPA for her contribution to the project. SCEC is funded by National Science Foundation (NSF) Cooperative Agreement EAR‐1600087 and USGS Cooperative Agreement G17AC00047. SCEC Contribution Number 13471. The work of W. Walter and C. N. Pennington was completed at LLNL under Contract DE‐AC52‐07NA2734. J. Zhang and H. Yang are supported by Hong Kong Research Grant Council (Awards 14306122 and 14308523).

Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

Data Availability

The common waveform database and associated metadata are described by Baltay et al. (2024), and are available for download at the Southern California Earthquake Data Center (SCEDC): https://scedc.caltech.edu/data/stressdrop-ridgecrest.html (last accessed October 2021). Along with full waveform data from stations within 1° of the earthquake locations (Fig. 1b), we have provided phase picks and metadata, including the Trugman (2020) catalog with updated SCSN magnitudes (https://service.scedc.caltech.edu/eq-catalogs/date_mag_loc.php; last accessed June 2024). For more details on the waveform data including stations and processing details, please refer to Baltay et al. (2024). All the waveform data and metadata references used in the analysis are publicly available (Baltay et al., 2024) and accessible from the SCEDC (SCEDC, 2013; doi: 10.7909/C3WD3xH1), Incorporated Research Institutions for Seismology (IRIS; https://ds.iris.edu/ds/nodes/dmc/, last accessed October 2021) and Northern California Earthquake Data Center (NCEDC; doi: 10.7932/NCEDC). The SCEDC and Southern California Seismic Network (SCSN) are funded through U.S. Geological Survey (USGS) Grant G20AP00037, and the Southern California Earthquake Center, which is funded by National Science Foundation (NSF) Cooperative Agreement EAR‐0529922 and USGS Cooperative Agreement 07HQAG0008. IRIS Data Services are funded through the Seismological Facilities for the Advancement of Geoscience and EarthScope (SAGE) Proposal of the NSF under Cooperative Agreement EAR‐1261681. Networks that provided data are: CE (California Geological Survey, 1972); CI (California Institute of Technology and U.S. Geological Survey [USGS] Pasadena, 1926); GS (Albuquerque Seismological Laboratory [ASL]/USGS, 1980); NN (University of Nevada, Reno, 1971); NP (USGS, 1931); PB (https://www.fdsn.org/networks/detail/PB/); SN (University of Nevada, Reno, 1992); and ZY, https://www.fdsn.org/networks/detail/ZY_1990/ (Cochran et al., 2020). All data referenced here are available at the SCEDC (SCEDC, 2013) at https://scedc.caltech.edu/data/stressdropridgecrest.html (last accessed October 2021), in which a “Quick‐reference guide” is also posted for more information on the waveform data. The SCSN catalog change history is available from https://scedc.caltech.edu/eq-catalogs/change-history.html (last accessed March 2025). The supplemental material contains a Fourier amplitude spectrum (FAS) flatfile, Figures S1 and S2, and Table S1, a zip folder of.csv for each author‐submission (56 total) at https://cloud.seismosoc.org/s/ksyAo2L8G8QaDnm (last accessed April 2025). Compiled results for the 56 events including the submitted corner frequency, best moment, and best magnitude for each method.

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