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Implications of the SCEC/USGS Community Stress Drop Validation Study for Physics-based and Empirical Ground Motion Modelling

Description: 

The problem of decomposing recorded waveforms into source, path, and site effects is fundamental to both earthquake source analysis and ground motion modeling (GMM). For this reason, the Statewide California Earthquake Center (SCEC)/U. S. Geological Survey (USGS) Community Stress Drop Validation study is relevant to, and dependent on, GMM. We present the findings of the Community Study, focusing on what we have learned about the statistical distribution as well as spatial and temporal variability of earthquake stress drop, a key input variable in non-ergodic empirical GMMs. Through the Community Study, we distributed a common dataset of earthquake records for the 2019 Ridgecrest Earthquake Sequence and to date have received 56 unique submissions of spectral corner frequencies, moment magnitudes, and spectral stress drops. While overall results reveal significant scatter of spectral stress drops among the different methods, we use this variability to quantify the epistemic uncertainty of stress drop for any one earthquake. We average over all the submitted results for a distribution of stress drops with magnitude, depth, time, location and other parameters. We demonstrate how stress drop parameters, and their variability can be used as inputs to physics-based ground motion simulations and to constrain non-ergodic terms in empirical GMMs, both as analogs to the event term and as direct modeling inputs in Fourier models. We highlight the tradeoffs in assumptions and constraints inherent in estimating any single parameter from recorded waveforms. In this case, the estimates of corner frequency and moment are highly dependent on the assumed attenuation and path models, a problem common to both source and ground-motion modeling. The full data set, including a ground-motion flat file, is now available to the broader community for continued study and use in GMM. The next stage of the community endeavor will likely involve synthetic data and we welcome new members to participate in any aspect. Visit https://www.scec.org/research/stress-drop-validation for more information.

Session: Challenges and Opportunities in Constraining Ground-motion Models from Physics-based Ground-motion Simulations - I

Type: Oral

Date: 4/17/2025

Presentation Time: 08:45 AM (local time)

Presenting Author: Annemarie

Student Presenter: No

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