Systematic Fault Plane Analysis in Complex Earthquake Sequences: Application to the 2019 Ridgecrest, CA and 2008 Mogul, NV Earthquakes

Christine J. Ruhl, & Rachel E. Abercrombie

Submitted August 14, 2020, SCEC Contribution #10565, 2020 SCEC Annual Meeting Poster #070

Earthquakes rupturing multiple faults and highlighting highly complex fault zone structures are often observed when good data coverage is available and advanced processing techniques are applied (e.g., earthquake relocation). The prevalence of these observations over the last decade suggests that multi-fault ruptures are a fundamental part of the earthquake process. Characterizing these zones at depth is therefore important for understanding earthquake processes from stress triggering to rupture dynamics – but quantitative characterization and comparison of these complex sequences is a challenge. Recently, machine learning methods that utilize waveform similarity have been used to improve catalog completeness and characterize focal mechanism changes before and after the largest events (e.g., Trugman et al., 2020). The high level of spatiotemporal complexity remains enigmatic, however, and despite developing high-resolution observations, most studies still simplify analysis by, e.g., using broad temporal or spatial divisions of the dataset. Other studies use visual interpretations of fault geometries to characterize trends in the fault zone. Here, we statistically cluster the relocated catalogs of two complex earthquake sequences and systematically quantify fault zone geometry. For each spatiotemporal cluster, we use a bootstrapping technique to identify fault orientation, dimension, and effective stress drop from the seismicity associated with it. We find good agreement between interpreted fault orientations identified visually in previous studies and our objectively identified cluster geometries. For the Mogul earthquake swarm, we also find remarkable spatiotemporal agreement between effective stress drops of foreshock clusters along the mainshock fault zone and the relative static stress drops of individual events. By delving into the details of complex sequences, we can better understand their evolution and the relationship between mainshocks and their associated seismicity.

Key Words

Ruhl, C. J., & Abercrombie, R. E. (2020, 08). Systematic Fault Plane Analysis in Complex Earthquake Sequences: Application to the 2019 Ridgecrest, CA and 2008 Mogul, NV Earthquakes. Poster Presentation at 2020 SCEC Annual Meeting.

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