SCEC Award Number 23108 View PDF
Proposal Category Workshop Proposal
Proposal Title Two 2023 Workshops for Year 3 of the Community Stress Drop Validation Study TAG
Investigator(s)
Name Organization
Annemarie Baltay United States Geological Survey Rachel Abercrombie Boston University Shanna Chu United States Geological Survey
Other Participants other TAG members (131 on mailing list)
SCEC Priorities 1d, 2d, 4a SCEC Groups Seismology, FARM, GM
Report Due Date 02/22/2024 Date Report Submitted 02/29/2024
Project Abstract
 The January 22, 2024 Stress Drop Validation TAG workshop entitled “Update and Looking Forward” was held virtually and was attended by 105 individuals, with three main themes, in three sessions. As always, we had lots of dedicated discussion time and welcomed broad community participation. In Session 1: Summary of Project, Wrapping Up and BSSA Special Issue we discussed the current status of the meta-analysis by Abercrombie and Baltay, had a round table from contributors as to their updates, and talked about the open BSSA Special Issue on Improving Measurements of Earthquake Source Parameters; at least 13 manuscripts are in preparation to be submitted. In Session 2: Wider purpose and Looking Forward we discussed how we have impacted the broader community, with an invited panel of stress drop users from the wider community who work on ground motion and hazards, source modeling, and earthquake physics, to comment on our work so far and what our priorities should be moving forward. In Session 3: Looking forward - Designing a Control Experiment using Synthetic seismograms, we discussed one option for the next portion of the community study - a “controlled” experiment using synthetic or simulated earthquake seismograms with known rupture parameters to estimate spectral stress drop, and other potential characterizations of source processes. We had presentations from several modelers of simulated datasets, and a discussion of which approach is most applicable to use as data for estimating stress drop. Ultimately, we need to discuss this topic more.
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. This supports SCEC Priority 4.1.3: Collaborative Earthquake Stress Drop and Source Study and furthermore meets the call for training the next generation of users, as we have successfully included many early career researchers and specifically involved stress drop users, who are not analysts, in the workshop.
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 Stress Drop Validation Community Project workshops have continually involved a broad audience and group of participants. To date, we have received results from 20 unique research groups for a total of 48 submissions, including groups from the US and Europe, with undergraduate and graduate students participating. The January 22, 2024 Stress Drop Validation TAG workshop was held virtually and was attended by 105 individuals, 64 of whom joined both morning and afternoon sessions, with participants from 20 countries and hailing from North America, South America, Europe, Africa, Asia, Oceania and India. 70% were from the United States. In between workshops, we hold ~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.
We strive to include early career researchers as invited presenters and panelists. At this workshop, invited panelists included Tara Nye (current graduate student), Hao Guo (postdoc) and Jamie Neely (postdoc) alongside mid and late career (including emeritus) researchers. We had lots of time set aside for discussion and encouraged many folks to speak up to avoid the same old voices. The results from the entire Stress Drop Validation TAG have been presented at many conferences, workshops, and seminars including the SCEC annual meeting, USGS Earthquake Science Center seminar, AGU annual meeting and SSA annual meeting, as well as other various departmental seminars.
Exemplary Figure Figure 1. All submitted corner frequencies for the selected 55 events, from 48 submissions, with different submissions/authors shown in different symbol shapes/colors. Average corner frequency in black circles, and best fit constant stress drop line in dashed. (left) initial submissions. (Right) Submissions adjusted with a per-author/per-submission trend removed. Trend is a function of magnitude and distance.
Linked Publications

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