Stress drop and ground-motion source comparison of the July 2019 Ridgecrest earthquake sequence: A community validation study

Annemarie S. Baltay, & Rachel E. Abercrombie

Published August 15, 2020, SCEC Contribution #10673, 2020 SCEC Annual Meeting Poster #073

We propose a community stress drop validation study using the 2019 Ridgecrest earthquake sequence as a common data set. Earthquake stress drops are notoriously variable and attempts to correlate estimates of the same earthquake using different methods or from different researchers have not always led to satisfactory results. Despite these challenges, earthquake stress drop remains a key parameter in many ground motion, rupture simulation, and source physics problems in earthquake science. We seek to understand the physical controls and methodological reasons for similarity or differences in stress drops and other source characterization parameters. The 2019 Ridgecrest earthquakes are part of well-recorded sequence, to date consisting of the M7.1 mainshock, M6.4 aftershock, 200+ aftershocks of M3.5+ and 10,000+ events greater than M1.0, recorded on up to 900 local, regional, and temporary seismic stations. We propose to launch the community comparison study in an organic manner by soliciting estimates of stress drop or high-frequency source characterization already completed and also encouraging others to become involved.

To start, we compare Arias intensity stress drops and high-frequency ground-motion event terms from Parker et al. (2020), the spectral decomposition stress drops from Trugman (2020), and the automated, single-station Brune spectral inversion results from Rekoske et al. (2019). Preliminary results do not find a strong correlation between any of the data sets, which prompts us to consider the data and methodological differences and uncertainties, as well as the physical controls on the events that have very different stress drops between data sets. Through understanding the relative contributions of the aleatory and epistemic components of variability, we aim to develop a robust methodology for estimating stress drop that reflects the true source processes, and guidelines for uncertainty quantification. We also consider what uncertainty is introduced when path and site effects are not fully considered, as is the case with the automated fits, compared to the more sophisticated spectral decomposition or empirical Green’s function approaches.

Finally, we encourage the community to contribute stress drop, radiated energy, high-frequency ground motion or source characterization results from the Ridgecrest sequence to our validation study. Anyone interested in participating in any way, please contact us.

Key Words
stress drop, Ridgecrest, community study, source characterization, high-frequency ground motion

Citation
Baltay, A. S., & Abercrombie, R. E. (2020, 08). Stress drop and ground-motion source comparison of the July 2019 Ridgecrest earthquake sequence: A community validation study . Poster Presentation at 2020 SCEC Annual Meeting.

Related Projects & Working Groups
Seismology