Mechanics and statistics of aftershaking during the 2019 Ridgecrest, CA sequence

Tim Clements, Elizabeth S. Cochran, Sarah E. Minson, Nicholas J. van der Elst, Clara E. Yoon, Annemarie S. Baltay, & Morgan T. Page

Submitted September 7, 2025, SCEC Contribution #14560, 2025 SCEC Annual Meeting Poster #TBD

Large earthquakes usually generate afterslip and a measurable increase in the rate of aftershocks in the seconds to days following rupture. However, catalog-based aftershock rates are difficult to measure in this interval because body, surface, and coda waves from successive earthquakes mask individual phases. Here, we introduce a mechanical and statistical model for aftershaking, which we define as the continuous seismic ground motion recorded in the seconds to days following a large earthquake. Immediately following an earthquake, aftershaking is easier to detect than aftershocks that are buried in the shaking of other events, and analyzing aftershaking requires less processing than assembling an earthquake catalog. Our rate-and-state based mechanical model links the amplitude of aftershaking to the velocity of afterslip and our statistical model for the combined distribution of seismic noise and aftershaking allows for the measurement of Omori decay parameters and Gutenberg-Richter b-values directly from continuous seismograms. We show that b-values extracted from continuous seismograms during the 2019 M7.1 Ridgecrest, CA earthquake sequence are consistent with b-values extracted from a high-resolution earthquake catalog and our measured Omori p-value matches that from the USGS operational aftershock forecast. Rapid estimation of aftershaking statistics could lead to faster forecasts of expected ground motion.

Key Words
ground motion, forecasting, statistics

Citation
Clements, T., Cochran, E. S., Minson, S. E., van der Elst, N. J., Yoon, C. E., Baltay, A. S., & Page, M. T. (2025, 09). Mechanics and statistics of aftershaking during the 2019 Ridgecrest, CA sequence. Poster Presentation at 2025 SCEC Annual Meeting.

Related Projects & Working Groups
Earthquake Forecasting and Predictability (EFP)