The effect of azimuthal variation on measured stress drop: a case study of the 2019 Ridgecrest sequence

Shanna Chu, Annemarie S. Baltay, & Rachel E. Abercrombie

Published September 10, 2023, SCEC Contribution #13285, 2023 SCEC Annual Meeting Poster #035

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 alternative sampling algorithm to improve the ability of spectral decomposition to resolve azimuthal variability.

Key Words
stress drop

Citation
Chu, S., Baltay, A. S., & Abercrombie, R. E. (2023, 09). The effect of azimuthal variation on measured stress drop: a case study of the 2019 Ridgecrest sequence. Poster Presentation at 2023 SCEC Annual Meeting.

Related Projects & Working Groups
Seismology