Preliminary comparative analysis of results submitted to the International SCEC/USGS Community Stress Drop Validation Study and future plans

Rachel E. Abercrombie, & Annemarie S. Baltay

Published September 8, 2024, SCEC Contribution #14022, 2024 SCEC Annual Meeting Poster #061

We present a comparative analysis of the 56 sets of results submitted to the first stage of the SCEC/USGS Community Stress Drop Validation study. The Community study has engaged a wide, international group focused on a common dataset of the 2019 Ridgecrest, California, earthquake sequence. The aim of the collaboration is to improve the quality of earthquake source parameter estimates and their uncertainties, enabling more reliable ground motion forecasting and facilitating a better understanding of earthquake source physics.

Each submission consists of spectral corner frequencies (or source durations), moment magnitudes (M), and spectral stress drops. Initial analysis reveals significant scatter of spectral stress drops spanning over six orders of magnitude. Different choices of inversion methods and assumed parameters result in different estimations of the source contributions to recorded seismograms, influencing the source parameters obtained from modeling these calculated source spectra. Correlation between corner frequency (fc) measurements from different methods within even a small M range is always better than that of spectral stress drop, because the fc measurements reflect the underlying decrease in fc with increasing M. We find no significant correlation of different earthquake measurements between methods for M≲2.5 indicating that obtaining reliable spectral stress drop values for events this small is difficult within the frequency range of the data. Considering the trends in M and depth for each set of submissions demonstrates method-dependent variations and some consistent trade-offs. Relative event-to-event variability is more consistent between different methods and more reliable than apparent overall trends, suggesting that real, physically-based variations in earthquake sources may be resolvable. We remove these method-dependent trends to examine any relation between the underlying spatial distribution and the M6.4 and M7.1 mainshock ruptures.

A Special Issue of the Bulletin of the Seismological Society is in progress that will include the results and community data of the first stage of this community endeavor, available for all to analyze. The next stage of the Community Study will likely include an experiment involving synthetic data. We welcome new members to the study that wish to observe, learn, or actively participate. Visit https://www.scec.org/research/stress-drop-validation for more information.

Citation
Abercrombie, R. E., & Baltay, A. S. (2024, 09). Preliminary comparative analysis of results submitted to the International SCEC/USGS Community Stress Drop Validation Study and future plans. Poster Presentation at 2024 SCEC Annual Meeting.

Related Projects & Working Groups
Seismology