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Characterizing Directivity in Small (M3-5) Aftershocks of the Ridgecrest Sequence

Description: 

A longstanding issue in source seismology is whether or not the variation in measured “stress drop” is due to methodological differences or physical assumptions, which leads to confounding results about predicted ground motion in regional earthquake hazards and source physics. The spectrum of seismic radiation is commonly used to derive the stress drop for earthquakes, which relates an earthquake’s source dimension to its ground motion. The first step in using the spectrum to estimate the stress parameter is to separate out source contributions in the raw data from site- and path- effects, which may be performed in various ways. In this study, we compare two common methods of deconvolving source spectra from waveform records: using a nonparametric matrix inversion (spectral decomposition) and using an empirical Green’s function (eGf) method. Using the example case of the 2019 Ridgecrest sequence, we classify source spectra into types based on observed spectral complexity, noting that complex spectral shapes (at both the event and station level) are more likely to yield variable estimates of the stress parameter when the deconvolution method differs. We show that source directivity can account for some amount of discrepancy in source parameter estimates between the two methods. Typically, azimuthal heterogeneity in path is not accounted for in a spectral decomposition, while eGf methods specifically account for specific paths. We present an approach to understand the variation in corner frequency due to azimuthal variability.

Session: Understanding and Quantifying the Variability in Earthquake Source Parameter Measurements [Poster Session]

Type: Poster

Date: 5/3/2024

Presentation Time: 08:00 AM (local time)

Presenting Author: Shanna

Student Presenter: No

Invited Presentation: 

Authors