SCEC Award Number 21114 View PDF
Proposal Category Workshop Proposal
Proposal Title Virtual Workshop for the Community Stress Drop Validation Study
Investigator(s)
Name Organization
Annemarie Baltay United States Geological Survey Rachel Abercrombie Boston University
Other Participants Proposed Community Stress Drop Validation Study TAG members
SCEC Priorities 2d, 1d, 4a SCEC Groups Seismology, FARM, GM
Report Due Date 12/04/2021 Date Report Submitted 12/02/2021
Project Abstract
 Workshop #1 “Stress Drop Validation – Planning and Preliminary Results” was held as a Zoom meeting on November 4, 2021, as part of the Community Stress Drop Validation TAG. The TAG is focused on understanding the nature and causes of discrepancies in earthquake stress drop, as well as where variability arises. We observe differences in stress drop estimates from different researchers, even when applying similar methods, and differences between methods and data selections, even when applied by the same researcher. These differences are often larger than the calculated uncertainties, making it hard and confusing to use these measurements for ground motion prediction and to study earthquake source physics.
The First Workshop, aimed at building the community of those who measure and those who use stress drop estimates, received 132 registrations, and 101 participants from 14 countries on 5 continents. Leading up to the workshop, 11 research groups submitted initial results from this dataset, of which, one was directly led by an undergraduate and four by graduate students.
Abercrombie and Baltay presented their initial meta-analysis of the individual results. Direct comparison of the reported stress drops reveals considerable scatter, which was not surprising, but perhaps some stronger correlation between results using similar methods.
By the conclusion of Workshop #1, the group agreed to focus on a subset of 50 earthquakes for future comparison. Many researchers became aware of others using similar and different methods, and have already reached out to start collaborations with one another to probe the effects of method details.
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 Workshop 1 was held as a Zoom meeting on November 4, 2021. Anyone currently working on, or interested in, the science questions noted above and/or learning about Ridgecrest earthquake studies was encouraged to apply to participate, especially researchers and young investigators. We received 132 registrations, and 101 participants from 14 countries on 5 continents. We solicited preliminary results estimating stress drop using the common dataset, and used those results in the workshop to start discussion. We received preliminary results from 11 groups, of which, one was directly led by an undergraduate and four by graduate students.
As one overarching goal for the workshop was simply to facilitate communication between different research groups and disciplines, and to build (and maintain) project momentum, we experimented with formats in different sessions, built in lots of time for discussion and breakout rooms, and had fewer long talks. We also worked to ensure a diverse group of speakers and moderators, prioritizing early-career researchers and gender equity; 1 speaker was an undergraduate, two were graduate students and 2 were post-docs. The decision to include both observational seismologists making measurements, and users of those measurements was clearly successful with both groups contributing and learning from one another. The workshop also proved beneficial to the many students who participated, looking to understand the problems and meet the community as they begin work in this field.
Following the workshop, we followed up with all the presenters and moderators for their feedback about the format and content of the workshop. As we had experimented with a variety of different talk and discussion formats, we were curious to see what had worked best. People were unanimously happy and excited about the workshop and felt they learned a lot and connected with many colleagues, new and old. Everyone enjoyed the lengthy discussion times and breakout rooms.
Exemplary Figure Figure 2. Initial submitted results for 22 events which were analyzed by 8 or more (out of 14) methods, plotted as estimated corner frequency vs catalog magnitude. Solid black dots are the log10 averaged across all methods; colors show the different estimates. Some events (smallest ML) show relatively less variability as compared to some of the larger events.
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