Systematic Measurements of Rupture Directivity for Small-to-Moderate Earthquakes in California
Description:
Rupture directivity is an important but poorly characterized earthquake source property that can have a direct effect on the azimuthal distribution of ground motions and hence earthquake hazard. Directivity has been measured for many moderate-to-large earthquakes in California, but systematic measurements for smaller earthquakes are needed to obtain a more complete picture of the underlying rupture and fault mechanisms that control directivity and amplified ground motion. Developed by Ross & Ben-Zion (2016) and expanded by Calderoni et al. (2023), the directivity index is a measure of azimuthal difference in the spectral ratio between a target event and a nearby empirical Green’s function (EGF) event, averaged over a frequency range spanning the target and EGF corner frequencies. Here, we generalize this approach by calculating the azimuthal distribution of the directivity index, which allows for inference of dominant rupture direction in cases where the rupture plane is unknown a priori. We apply this technique to assess spatiotemporal patterns in rupture directivity characteristics for small earthquakes throughout California that are well-recorded by recent network expansions in the state. We use synthetic tests to establish the quantitative relation between directivity index measurements and physical rupture properties, and also develop a system for ranking the quality of each EGF or combination of EGFs used in the measurements to improve the robustness of the results. Preliminary results show success for small-to-moderate strike-slip earthquakes in the San Jacinto Fault Zone, and we aim to expand that work to include M3+ events in throughout the state, as well as test the method on earthquakes in dip-slip regimes.
Session: Characteristics and Mechanics of Fault Zone Rupture Processes, from Micro to Macro Scales [Poster Session]
Type: Poster
Date: 5/2/2024
Presentation Time: 08:00 AM (local time)
Presenting Author: Anne
Student Presenter: Yes
Invited Presentation:
Authors
Anne Patton Presenting Author Corresponding Author ampatton@nevada.unr.edu University of Nevada, Reno |
Daniel Trugman dtrugman@unr.edu University of Nevada, Reno |
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Systematic Measurements of Rupture Directivity for Small-to-Moderate Earthquakes in California
Category
Characteristics and Mechanics of Fault Zone Rupture Processes, from Micro to Macro Scales