SCEC2025 Poster #036: Distinguishing Spatial Variations in California Earthquake Dynamics Using a High- to Low-Frequency Spectral Ratio

Group B, Poster #036, Seismology

Distinguishing Spatial Variations in California Earthquake Dynamics Using a High- to Low-Frequency Spectral Ratio

Ian Vandevert, Peter M. Shearer, & Wenyuan Fan

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Poster Presentation

2025 SCEC Annual Meeting, Poster #036, SCEC Contribution #14732 VIEW PDF

Earthquakes radiate varying amounts of high-frequency energy, reflecting differences in source dynamics, propagation and attenuation, and near-station site effects. Identifying source variations is essential for understanding spatial differences in earthquake mechanics; however, isolating the source effects can be challenging. Conventional approaches typically rely on idealized rupture models and empirical path corrections to estimate earthquake stress drop, yielding results that are hard to compare consistently among different groups and datasets. In this study, we apply a new data-driven approach to measure differences in spectra directly from the observations. We compute a ratio of high-f...requency to low-frequency amplitude from individual spectra. By empirically correcting the path, station, and magnitude effects, we measure the relative amount of high-frequency radiation in an earthquake compared to a group of nearby events. Our results show that this new measurement is correlated with earthquake stress drop estimates from previous studies of the 2019 Ridgecrest aftershock sequence, suggesting that it can be used to infer differences in source dynamics. We plan to expand this approach to examine California seismicity statewide to identify spatial differences in high-frequency radiation and inferred source mechanics, and compare to other geophysical parameters such as earthquake depth and focal mechanism. This large-scale study of spatial differences in earthquake radiation offers an observation-based alternative to traditional stress-drop estimation methods, and we plan to explore its implications for fault properties and strong ground motion prediction in California.
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