SCEC Award Number 22042 View PDF
Proposal Category Collaborative Proposal (Integration and Theory)
Proposal Title Continuation of a Technical Activity Group for the Community Stress Drop Validation Study using the 2019 Ridgecrest Earthquake Dataset
Name Organization
Annemarie Baltay United States Geological Survey Rachel Abercrombie Boston University Christine Ruhl University of Tulsa Taka'aki Taira University of California, Berkeley Xiaowei Chen University of Oklahoma
Other Participants
SCEC Priorities 1d, 2d, 4a SCEC Groups Seismology, FARM, GM
Report Due Date 03/15/2023 Date Report Submitted 04/13/2023
Project Abstract
We report on the progress in Year 2 (2022) of the Community Stress Drop Validation Technical Activity Group (TAG). The TAG seeks to understand the physical controls and methodological reasons for similarity or differences in estimates of earthquake stress drops, so that they can be used reliably by the earthquake science community. Under the TAG, many researchers from the community independently calculate and submit stress drop estimates using a consistent dataset of the 2019 Ridgecrest sequence of earthquakes. In its first two years, the TAG has gained huge global momentum, with nearly 150 members on the mailing list, 101 participants at virtual Workshop #1, 30 in-person participants at Workshop #2 at the SCEC Annual Meeting in 2022, and 76 people at virtual workshop #3 in January 2023. In Year 1, we put together and distributed this common data set of ~13,000 earthquakes recorded on ~100 stations from the 2019 Ridgecrest sequence, and associated metadata, that participants have been using for analysis have received a total to date of 28 submissions from 18 research groups. The TAG activities are three-fold: (1) Coordination of the study and generation and upkeep of a common dataset; (2) Analysis of the common dataset to estimate stress drops; and (3) Meta-analysis of the resulting stress drops to understand their correlation or why differences arise. As the TAG developed, it became clear it is also serving a real need in informing potential users of stress drop-type measurements what they should be careful about and how to understand published stress drop values, when incorporating them into their own work.
Intellectual Merit SCEC seeks to understand both the characteristics and uncertainty of earthquake stress drop as it relates to basic source physics, rupture modeling and ground motion prediction, and has a focus on collaborative stress drop studies under Seismology Research Priority 4.1.3: Collaborative Earthquake Stress Drop and Source Study. This TAG specifically meets this research priority.
The motivation for the SCEC Community Stress Drop Validation TAG is focused on understanding the nature and causes of discrepancies in earthquake stress drop, as well as where random and physical variability arises. In this context, the main goals for the TAG are to use a common data set of records from the 2019 Ridgecrest earthquake sequence (consisting of over 12,000 events of M1 to M7.1) to address the questions:
● How do differing methods and model assumptions affect stress drop estimates?
● How do different researchers approach similar methods?
● How do data quantity, quality, selection and processing affect stress drop estimates?
● How do physical source (mechanism, depth, radiation pattern, directivity), path (geometrical spreading, attenuation), and site (soil conditions, site attenuation) features affect the estimates?
● What measurements, and uncertainties, would be most useful for the broader community?
Broader Impacts Through outreach and use of virtual platforms, we have been able to create a large, diverse, global community interested in resolving the issue of stress drop estimation. For example, we regularly hold our monthly Zoom calls twice in the same day, approximately 8 hours apart, to draw global participation (including researchers from the US, Europe, Japan, Israel, Saudi Arabia, Korea, Taiwan, and Columbia). The monthly Zooms are also popular for students and early-career researchers as they can comfortably listen in and are given opportunities to introduce themselves, share their work, and meet the other participants. Six early-career researchers who have submitted results to the project are taking the lead convening a project-focused special session at the 2023 Seismological Society of America Annual Meeting. To date, of the 28 submitted results, one was directly led by an undergraduate and four by graduate students. We also received submission of four results from groups in Europe. Graduate student Neupane was directly funded by this SCEC Award to work on the TAG project and attend the 2022 AGU Fall Meeting in Chicago in person, where he participated in career development workshops and met with collaborators. At workshops, our keynote talks are by early-career researchers: Colin Pennington (postdoc) at Workshop #1, Hao Guo (postdoc) at Workshop #2, and Jamie Neely (postdoc) at Workshop #3. Our in-person Workshop #2 in Palm Springs drew attendees who had not attended the SCEC annual meeting ever (or in a long while), so the TAG is helping to broaden SCEC participation.
New this year, we will offer special sessions for students, early career, and those new to stress drop, as part of the monthly Zoom calls as well as the workshops. We have had many inquiries from scientists who wish to be able to estimate stress drops themselves or be able to understand better under the hood what the methods do. At the in-person Workshop #4, we will host a several-hour hands-on tutorial of how to actually run at least two different stress drop estimation methods (namely an eGf deconvolution and generalized inversion method), led by some of our researchers who have developed and worked on these methods. To accompany this longer in-person live tutorial, we will have some 1-hour Zooms on more specific topics leading up to the workshop, such as how to preprocess seismic data and create Fourier spectra, how to determine window lengths, how to choose an eGf event. Through these specific events, we hope to continue to encourage and engage with students, postdocs and other early career researchers who wish to learn more about stress drop and remove some of the mystery.
Exemplary Figure Figure 1. Corner frequency and seismic moment (Mo) submitted by different authors (shown anonymously as different symbols) for Workshop #3 in January 2023. Corner frequency (fc) submitted (top row) and shown normalized by removing a single offset value for each author (bottom), compared to the estimated submitted Mo (left) and catalog magnitude (right). A reduction in scatter is evident when adjusting for each author, and tradeoff between fitted fc and Mo compresses the scatter in left panels as compared to right panels.

Results provided by research groups led by: Ian Vandevert, Peter Sherer, Dino Bindi, Xiaowei Chen, Emma Devin, Shanna Chu, Mariano Supino, Claudio Satriano, Tom Eulenfeld, Kevin Mayeda, Chen Ji, Bill Ellsworth, Killian Kemna, Meichen Liu, Christine Ruhl, Oliver Boyd, Haoran Meng, Doug Dreger and Annemarie Baltay.