How is fault complexity linked to high-frequency radiation from Southern California earthquakes?

Shanna Chu, Annemarie S. Baltay, Victor C. Tsai, Rachel E. Abercrombie, Greg Hirth, & Daniel Trugman

Submitted September 11, 2022, SCEC Contribution #12251, 2022 SCEC Annual Meeting Poster #037

Fault complexity has been linked to enhanced high frequency radiation in earthquakes, but the specific relationships between earthquake source complexity, the radiated spectrum and what kind of physical mechanisms are involved are still not well understood. Moreover, several types of fault complexity exist, but extant metrics, such as surface roughness, do not well describe complexity due to interactions between multiple interacting faults. We are interested in the effects of fault complexity that arise from multi-fault systems, where earthquakes have been observed displaying consistent spatial spectral variations on the scales of kilometers. In one study using surface fault maps, we define new metrics of quantifying the complexity of groups of faults within selected polygonal regions, based on the projected orientations and densities of the faults, which are assumed to be self-similar. Here we find that enhanced high-frequencies in observed earthquake spectra from the broader Southern California region tend to correlate with locally misaligned faults having disordered orientations, suggesting that structural interactions between different parts of the fault system may play a role in generating the ground motions felt during earthquakes. Focusing on a smaller study area of the 2019 Ridgecrest earthquake and its aftershocks, we examine variations in spectral shape without constraining any particular source model. We use shape similarity clustering to classify several families of spectra, which have correlations to the location and depth of the events, thus linking spectral shape type to different metrics of spatial complexity. Our observations reinforce several physical mechanisms at the source level, such as meter-scale structural collisions or stress heterogeneity, which can affect the amount of high frequencies produced by earthquakes, and suggest ways to incorporate spatial structure in future ground motion studies.

Key Words
fault complexity, source processes

Chu, S., Baltay, A. S., Tsai, V. C., Abercrombie, R. E., Hirth, G., & Trugman, D. (2022, 09). How is fault complexity linked to high-frequency radiation from Southern California earthquakes? . Poster Presentation at 2022 SCEC Annual Meeting.

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