Using a High- to Low-frequency Spectral Ratio to Distinguish Variations in Earthquake Source Properties
Description:
Earthquakes radiate energy across a range of frequencies and the shape of the source spectrum can reveal details about earthquake mechanics. However, interpreting observed spectra is complicated by hard-to-resolve tradeoffs between source and path effects, i.e., an earthquake with less high-frequency energy might have the same observed spectrum as an earthquake whose waves passed through a more attenuating region. Often, analyses that attempt to correct observed spectra for path and site effects to estimate parameters like stress drop suffer from large uncertainties and show poor agreement among different studies. Here, we introduce a method to address this ambiguity by studying a new parameter, β, defined as the ratio of the average spectral amplitude in a high-frequency band to that in a low-frequency band. For a single station and sufficiently distant earthquake region, the path and station effects are roughly constant and are removed by applying a correction using small, local calibration events. Variation in corrected β values for earthquakes of similar magnitude therefore reveals changes in source mechanics. We identify spatial variations in corrected β values for southern California seismicity that correlate with spatial distributions of stress drop; since higher stress drop regions have comparatively more high-frequency radiation for equal magnitude earthquakes, they have a higher β. Our simple approach can robustly identify variations in high-frequency energy from different source regions without the need to apply path corrections, as the results are insensitive to path effects. Thus, our proposed β analysis provides an alternative to more complicated spectral analysis methods, such as spectral decomposition, for identifying variations in high-frequency radiation. We compare our results for different datasets to those of previous stress-drop studies, explore some synthetic examples, and discuss implications for earthquake dynamics and fault properties.
Session: Advances in Reliable Earthquake Source Parameter Estimation [Poster]
Type: Poster
Date: 4/16/2025
Presentation Time: 08:00 AM (local time)
Presenting Author: Ian
Student Presenter: Yes
Invited Presentation:
Poster Number: 37
Authors
Ian Vandevert Presenting Author Corresponding Author ivandevert@ucsd.edu University of California, San Diego |
Peter Shearer pshearer@ucsd.edu University of California, San Diego |
Wenyuan Fan wenyuanfan@ucsd.edu University of California, San Diego |
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Using a High- to Low-frequency Spectral Ratio to Distinguish Variations in Earthquake Source Properties
Category
Advances in Reliable Earthquake Source Parameter Estimation