Does Fault Network Complexity Explain Stress Drop Variability?

Jaeseok Lee, Victor C. Tsai, Greg Hirth, Daniel T. Trugman, & Avigyan Chatterjee

Published September 10, 2023, SCEC Contribution #13271, 2023 SCEC Annual Meeting Poster #115 (PDF)

The geometry of fault systems can significantly affect earthquake rupture processes and the resulting ground motions. While numerous studies have focused on identifying the effects of fault roughness, recent findings highlight the often overlooked importance of larger-scale geometric complexities, which include bends, gaps, and stepovers within networks of faults. In particular, fault network complexity has been proposed to cause high-frequency earthquake ground motions (Tsai and Hirth, 2020; Tsai et al. 2021), and observations in Southern California have shown positive correlations between the degree of fault network complexity and enhanced high-frequency seismic radiation, characterized in terms of measured stress drops (Chu et al. 2021). In this study, we expand on these previous findings by examining a wider range of geographic regions with different scales and multiple stress drop catalogs.

We demonstrate the correlation between fault network complexity and earthquake stress drops in our analysis of fault networks in Southern California, Japan, and Central Italy. Using high-resolution surface fault traces in these regions, we mapped fault misalignment and density as metrics of fault network complexity. We identified zones of coherent fault network characteristics through sensitivity tests across different length scales. For each earthquake recorded in the published stress drop catalogs, we estimated the local fault misalignment and density. In agreement with previous studies, consistent positive correlations between fault complexity metrics and stress drops were found in all three regions. The trends show some variability depending on the different methods used to estimate the earthquake stress drops. In general, the positive correlation between stress drop and fault misalignment is stronger than that between stress drop and fault density. Our findings provide additional evidence supporting the hypothesis that elastic collisions between discrete structures within networks of misaligned faults can lead to enhanced high-frequency seismic radiation. By establishing links between measurable aspects of fault geometry and seismological observations, we may demonstrate that there is a contribution from complex fault zones that is not easily explained with traditional earthquake models.

Citation
Lee, J., Tsai, V. C., Hirth, G., Trugman, D. T., & Chatterjee, A. (2023, 09). Does Fault Network Complexity Explain Stress Drop Variability?. Poster Presentation at 2023 SCEC Annual Meeting.

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)