Leveraging Multi-Phase and Multi-Method Spectral Ratio Analysis for Robust Stress Drop Estimation
Trey C. Knudson, William L. Ellsworth, Gregory C. Beroza, & Bruce E. ShawSubmitted September 7, 2025, SCEC Contribution #14826, 2025 SCEC Annual Meeting Poster #TBD
Source, path, and site effects can introduce spectral complexities that make it challenging to accurately measure earthquake source parameters such as stress drop. Building on the asymptotic spectral ratio approach of Shaw et al. (2016) and Walter et al. (2017), we explore whether combining spectral measurements from multiple seismic phases can reduce spectral complexity to produce smoother, more reliable asymptotes. We compute spectral ratios for co-located event pairs from the Ridgecrest sequence using three distinct estimation methods — multitaper, multiwindow, and envelope analysis — applied to P waves, S waves, and coda waves. This multi-phase, multi-method framework allows us to directly compare how different phases and estimation approaches influence spectral shape and asymptote stability, with the premise that even if their corner frequencies differ, their low- and high-frequency limits should converge. Preliminary results indicate that while individual phase–method combinations yield broadly consistent asymptotes, their differences can be leveraged to reduce high-frequency variability. In particular, coda-wave measurements appear to mitigate spectral bumps in the high-frequency limit, complementing the higher resolution of direct P and S waves. Ongoing work will quantify the smoothness and inter-method consistency of asymptote estimates, with the goal of improving stress drop ratio measurements for event pairs.
Citation
Knudson, T. C., Ellsworth, W. L., Beroza, G. C., & Shaw, B. E. (2025, 09). Leveraging Multi-Phase and Multi-Method Spectral Ratio Analysis for Robust Stress Drop Estimation. Poster Presentation at 2025 SCEC Annual Meeting.
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Seismology
