Spatial variations in the source spectra of Southern California earthquakes
Description:
We show observed variations of earthquake spectra in Southern California earthquakes which support several physical mechanisms for source-level complexity. The spectrum of seismic radiation from earthquakes are usually fit to a model derived from an analytical crack solution. However, real earthquakes are observed to have complex radiated spectra. This becomes problematic for hazard estimation when parameters related to ground motion, such as earthquake stress drop, cannot be accurately estimated due to this complexity. Complexity of waveform recordings can be attributed to various physical mechanisms in the earthquake source itself. In our recent study, we defined new metrics using fault maps to quantify the complexity of groups of faults within selected polygonal regions, specifically attempting to capture the possibility that faults in a complex network could interact. We found that enhanced high-frequencies in observed earthquake spectra from the broader Southern California region tend to correlate with locally misaligned faults having disordered orientations, suggesting that structural interactions between different parts of the fault system may play a role in generating the ground motions felt during earthquakes. Focusing on a smaller study area of the 2019 Ridgecrest earthquake and its aftershocks, we examine variations in spectral shape that arise from using differential methods to deconvolve source spectra from the observed waveform (which includes effects from the source, wave propagation, and station site response). These variations show that spatial patterns of spectra variability continue from the fault-map scale to a more local scale, and also may have an azimuthal dependence. Our observations support several physical mechanisms of spectral complexity at the source level, such as meter-scale structural collisions or stress heterogeneity, which can affect the amount of high frequencies produced by earthquakes.
Session: Understanding the Variability in Earthquake Stress Drop Measurements [Poster]
Type: Poster
Date: 4/20/2023
Presentation Time: 08:00 AM (local time)
Presenting Author: Shanna Chu
Student Presenter: No
Invited Presentation:
Authors
Shanna Chu Presenting Author Corresponding Author schu@usgs.gov U.S. Geological Survey |
Annemarie Baltay abaltay@usgs.gov U.S. Geological Survey |
Rachel Abercrombie rea@bu.edu Boston University |
Victor Tsai victor_tsai@brown.edu Brown University |
Greg Hirth greg_hirth@brown.edu Brown University |
Daniel Trugman dtrugman@unr.edu University of Nevada, Reno |
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Spatial variations in the source spectra of Southern California earthquakes
Category
Understanding the Variability in Earthquake Stress Drop Measurements