Exploring the Cross-Fault Rupture Zone of the 2020 Mw 6.5 Monte Cristo Range Earthquake of the Central Walker Lane

Patricia Persaud, Joses B. Omojola, Rufus D. Catchings, & Mark R. Goldman

Submitted September 7, 2025, SCEC Contribution #14690, 2025 SCEC Annual Meeting Poster #TBD

The Walker Lane and Eastern California Shear Zone can be considered a natural laboratory outside the most populated regions of California to investigate issues of seismicity and fault mechanics, which are important for understanding the seismic hazard in California (Wesnousky, 2024). The 15 May 2020 Mw 6.5 Monte Cristo Range earthquake occurred in the California-Nevada border region. The earthquake occurred on a previously unmapped fault in the Central Walker Lane and was a cross-fault rupture, whereby two faults cross one another and ruptured together in the mainshock. The USGS rapidly deployed a 60-station, three-component nodal array to monitor the aftershock sequence, and data were recorded for one month following the mainshock at a 500 Hz sampling rate. Using two machine-learning-based methods for event detection and phase picking (i.e., the MUnet model of Omojola and Persaud (2024) and EQTransformer (Mousavi et al., 2020)), we first produce and refine a catalog of the aftershocks. The seismograms were resampled to 100 Hz and fed through the pretrained neural networks, and phase detections at 10 or more stations were classified as events. Our preliminary results show that >19K events occurred in the 1-month period. We relocated the initial dataset using the double-difference relocation method to improve event locations. Our final earthquake catalog provides dense ray-path coverage across the aftershock area. We combine a subset of the phase picks in our catalog with recordings of earthquakes and mine blasts at stations in the surrounding area to produce large-scale (~300 km x 225 km area) P- and S-wave velocity models for the Central Walker Lane and refine these models on a finer grid in the smaller source region of the Monte Cristo Range event to examine in detail the structural complexity of the aftershock region. Our multiscale 3-D Earth model reveals crustal faults and shallow sedimentary basins, highlighted by major velocity contrasts. We also discuss methods to incorporate Bouguer gravity data and recent USGS high-resolution airborne magnetic data in the subsurface imaging of under-instrumented regions, such as the California-Nevada border.

Key Words
cross-fault rupture, Walker Lane, Monte Cristo Range sequence, multiscale velocity model

Citation
Persaud, P., Omojola, J. B., Catchings, R. D., & Goldman, M. R. (2025, 09). Exploring the Cross-Fault Rupture Zone of the 2020 Mw 6.5 Monte Cristo Range Earthquake of the Central Walker Lane. Poster Presentation at 2025 SCEC Annual Meeting.

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