SCEC Award Number 22101 View PDF
Proposal Category Workshop Proposal
Proposal Title Two 2022 Workshops for the Community Stress Drop Validation Study TAG
Investigator(s)
Name Organization
Annemarie Baltay United States Geological Survey Rachel Abercrombie Boston University
Other Participants Other TAG participants
SCEC Priorities 1d, 2d, 4a SCEC Groups Seismology, FARM, GM
Report Due Date 02/27/2023 Date Report Submitted 02/16/2024
Project Abstract
 The September 2022 Stress Drop Validation TAG workshop was held in person at the Hilton Palm Springs on Saturday September 10, prior to the SCEC Annual Meeting. The workshop was relatively focused, with the aim of engaging those who make stress drop measurements in detailed discussion and comparison of the submitted results from the various methods. 24 people attended in person, with an additional 6 active on Zoom. We received results of estimated stress drop, for a total of 21 submissions by various research groups.
The January 26, 2023 Stress Drop Validation TAG workshop was held virtually on Zoom from 9am to 3pm, attended by 76 people. By Workshop 3 in January 2023, we received several new and some updated submissions for a total to date of 28 submissions from 18 research groups. This workshop was meant to appeal to a broader audience, and so we had a set of two panels on uses of stress drop: Ground motion and hazard; and earthquake source physics.
At each of the two workshops, Abercrombie, Baltay and Chu presented meta-analysis of the individual results, focused on the selected events for comparison. By adjusting for an author-dependent bias, we see definite trends between different events, as well as indications of physical complexity manifesting as disagreement in estimated parameters between authors.
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 The first workshop was held in person in Palm Springs, and attracted 30 participants, 6 of whom were able to participate on Zoom. At least three of those participants flew in from outside of the US, and many participants had never been to a SCEC meeting (or hadn’t been in a very long time). The second workshop, held in January 2023, was fully virtual and thus we had more participants, 76, from many global locations including Japan, Europe, Israel and Saudi Arabia.
Leading up to each workshop, we have held ~monthly Zoom meet ups. Each time, we host the Zoom calls at two different times of day (usually in the morning and evening Pacific time) to enable researchers from around the globe to join. We have been successful in getting participants from Australia, Hong Kong, Taiwan, Japan, Colombia, Mexico, Europe, Israel and Saudi Arabia. Thus, we have been able to create a large, diverse, global community interested in resolving the issue of stress drop estimation.
At the first workshop, we had only one invited talk, from Hao Guo, a graduate student. At the second, we had one main invited talk from Jamie Neely, a postdoc. We invited and encouraged all participants to present their ideas as short talks or slide sets. We left a lot of time for discussion, and encouraged folks to mix at lunch, to foster the community.
We have now received results for 28 methods from 18 unique research groups, of which, one was directly led by an undergraduate and four by graduate students. We also received submission of four results from groups in Europe.
The aims and results of the first workshop were presented at a plenary session of the main SCEC meeting, and ~40 people also attended the follow-up zoom sessions we hosted to update the wider community.
Exemplary Figure Figure 1. Corner frequency and seismic moment (Mo) submitted by 18 different authors (shown anonymously as different symbols) for Workshop #3 in January 2023, for a total of 28 different submissions. 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 normalizing for each author, and tradeoff between fitted fc and Mo compresses the scatter in left panels as compared to right panels.