SCEC Award Number 23116 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Systematic Measurements of Rupture Directivity for California Earthquakes Using Bayesian Spectral Inference
Investigator(s)
Name Organization
Daniel Trugman University of Nevada, Reno
Other Participants Annie Patton (Graduate Research Assistant)
SCEC Priorities 2d, 4a, 3d SCEC Groups Seismology, FARM, GM
Report Due Date 03/15/2024 Date Report Submitted 03/12/2024
Project Abstract
 We develop a generalized workflow for measuring earthquake rupture directivity for small and moderate earthquakes. The technique is based on systematic analysis of azimuthal variations in spectral ratios between target earthquakes and nearby empirical Green’s function events. We demonstrate the promise of this method through characterization of seismicity in the San Jacinto Fault Zone, and will soon apply it to characterize seismicity throughout California. This project supported a 2nd-year PhD student in gaining experience in advanced seismic data analysis and will form a chapter of her thesis.
Intellectual Merit Directivity is a fundamental earthquake source parameter with important physical and practical implications, but it is difficult to measure systematically and at scale. The method we develop holds just such a promise, and we are well on our way toward such systematic characterization in California. With a large body of directivity measurements in hand, we can then systematically test different hypotheses about rupture dynamics and better understand hazard implications of any systematic trends we uncover.
Broader Impacts This project supported a 2nd-year PhD student in a chapter of her thesis, gaining research experience in seismology, data processing, and geophysical interpretation that will be foundational in her scientific career going forward. The work will be presented at the Seismological Society of America annual meeting in Spring 2024 and will evolve into a peer reviewed manuscript in the near future. The technique we have developed builds on prior work in this field and is general enough that it can be applied to any fault zone of interest with sufficient station coverage. We are working on a user-friendly software package to publish on GitHub for others to leverage our work.
Exemplary Figure Figure 3. Directivity measurements for M3.8 Event 38355456. (a) Directivity for two EGFs. A M2.2 EGF is on the left, and a M2.9 EGF is on the right, with maps below showing the event focal mechanisms and recording stations. (b) Rose diagram showing DI measurements for all quality EGFs (blue) and the weighted DI (bolded red). The red dashed lines show statistically significant values of the directivity index at the 95% and 99% levels.