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

Rachel E. Abercrombie, Annemarie S. Baltay, Shanna Chu, Taka'aki Taira, Dino Bindi, Oliver S. Boyd, Xiaowei Chen, Elizabeth S. Cochran, Emma G. Devin, Douglas S. Dreger, William L. Ellsworth, Wenyuan Fan, Rebecca M. Harrington, Yihe Huang, Killian Kemna, Meichen Liu, Adrien Oth, Grace A. Parker, Colin N. Pennington, Matteo Picozzi, Christine J. Ruhl, Peter M. Shearer, Daniele Spallarossa, Daniel T. Trugman, Ian Vandevert, Qimin Wu, Clara E. Yoon, & Ellen Yu

Submitted July 1, 2024, SCEC Contribution #13471

We present initial findings from the ongoing Community Stress Drop Validation Study to compare 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 significantly across studies for individual earthquakes.
Sponsored jointly by the U.S. Geological Survey and the Southern/Statewide 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 M1 to 7 during a two-week period of the 2019 Ridgecrest sequence, recorded within a 1-degree radius.
In this initial paper, 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 a minimal sample standard deviation of stress drop, indicating overall consistency in recovered spectral stress drop values.

Citation
Abercrombie, R. E., Baltay, A. S., Chu, S., Taira, T., Bindi, D., Boyd, O. S., Chen, X., Cochran, E. S., Devin, E. G., Dreger, D. S., Ellsworth, W. L., Fan, W., Harrington, R. M., Huang, Y., Kemna, K., Liu, M., Oth, A., Parker, G. A., Pennington, C. N., Picozzi, M., Ruhl, C. J., Shearer, P. M., Spallarossa, D., Trugman, D. T., Vandevert, I., Wu, Q., Yoon, C. E., & Yu, E. (2024). Overview of The SCEC/USGS Community Stress Drop Validation Study Using the 2019 Ridgecrest Earthquake Sequence. Bulletin of the Seismological Society of America, (submitted).

Related Projects & Working Groups
Community Stress Drop Validation