Routine Mw,coda Calculation for Small Earthquakes in Utah
Description:
Measuring Mw for small earthquakes is desirable in order to have a uniform magnitude catalog to compute accurate catalog statistics, such as b-value, and for earthquake hazard analysis. However, Mw is difficult or impossible to compute for events with Mw < 3.5 using traditional regional moment tensor analysis. An alternative is the S-wave coda Mw,coda method outlined in Mayeda et al. (2003). Mw,coda measurements are very stable due to the coda waves’ relative insensitivity to source radiation pattern and path heterogeneity. The Mw,coda method has been used to measure Mw in diverse regions worldwide, including the entire state of Utah as well as a more focused study of the March 2020 Mww 5.7 Magna, UT earthquake and its aftershocks (Holt et al., 2021). Mw,coda is effective for small magnitude earthquakes, down to approximately Mw,coda 1.5 in Utah. Currently, no seismic network calculates Mw,coda routinely.
Here we outline the process for calculating routine Mw,coda for Utah earthquakes with ML > 2.0 and depth > 0 km in the UUSS catalog. We calculate Mw,coda for such events from 2012 to present, and going forward will routinely calculate Mw,coda on a daily or weekly basis. Shallow events are eliminated from the analysis because their Mw,coda tend to be unreliable and overestimated due to an Rg-to-S scattering “bump” in the low frequency spectra. While this phenomenon makes measuring Mw,coda difficult for shallow events, it could perhaps be used as a depth discriminant. We rely on several quality checks before adding an Mw,coda to the catalog, including verification that the corner frequency is within the measured frequency range, and magnitude comparisons to ML and Me. Finally we calculate b-value using the traditional Gutenberg-Richter method as well as the more recent b-positive (van der Elst, 2021) for our new Mw,coda catalog and compare to ML b-values for the same events.
Session: Network Seismology: Recent Developments, Challenges and Lessons Learned
Type: Oral
Date: 4/20/2023
Presentation Time: 10:30 AM (local time)
Presenting Author: Katherine M. Whidden
Student Presenter: No
Invited Presentation:
Authors
Katherine Whidden Presenting Author Corresponding Author katherine.whidden@utah.edu University of Utah |
Andreas Cordova andreascordova98@yahoo.com University of Utah |
Ben Baker u6024448@gcloud.utah.edu University of Utah |
Kristine Pankow kris.pankow@utah.edu University of Utah |
Kevin Mayeda kevin.mayeda@gmail.com Air Force Technical Applications Center |
William Walter walter5@llnl.gov Lawrence Livermore National Laboratory |
Justin Barno barno1@llnl.gov Lawrence Livermore National Laboratory |
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Routine Mw,coda Calculation for Small Earthquakes in Utah
Category
Network Seismology: Recent Developments, Challenges and Lessons Learned