SCEC Award Number 22027 View PDF
Proposal Category Collaborative Proposal (Integration and Theory)
Proposal Title Seismic Moment and Corner Frequency of Ridgecrest Earthquakes Determined with Two Novel Methods
Investigator(s)
Name Organization
William Ellsworth Stanford University
Other Participants Trey Knudsen (graduate student)
SCEC Priorities 1d, 4a, 2d SCEC Groups FARM, Seismology
Report Due Date 03/15/2023 Date Report Submitted 06/28/2024
Project Abstract
 We look at two different methods of analyzing stress drops in the Ridgecrest sequence as part of the SCEC Community Stress Drop Validation Study. We employ a time-domain pproach to measure the spectrum of S-waves and apply it to both a spectral fitting and an asymptotic spectral ratio workflow. Both methods offer distinct advantages and are used to measure relevant stress drop parameters. We find that the propagation approach effectively determines moments across all magnitudes given enough stations. Preliminary results of the asymptotic spectral ratio approach show promising ability to reduce uncertainties and evaluate earthquakes of similar size.
Intellectual Merit This research tested and further developed a novel method for routine measurement of earthquake source properties (seismic moment and corner frequency) that is easy to apply and suited for incorporation in network operational workflow. It presents a straightforward method for routine measurement of moment magnitude and stress drop for virtually all earthquakes in the SCEC catalog from the digital era, and as such provides a rich new source of information on source excitation and seismic wave attenuation.
Broader Impacts This project is contributing significantly to the thesis research of the student, as well as to the SCEC/USGS Source Validation study using the Ridgecrest earthquake dataset.
Exemplary Figure Figue 3. Stress drop results using the Brune model. Single event results (left) for the entire Ridgecrest data set show a suggestion of scaling with seismic moment. Because we also observe a trend of increasing seismic moment with focal depth (middle), we cannot be certain at this stage if the scaling is real or due to unmodeled effects on the seismogram, including depth dependent attenuation in the crust. The single event and spectral ratio methods, however, agree well with each other (right), indicating that the precision of the measurement should be sufficient to ultimately resolve the scaling question
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