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## Comparing EGF Methods for Estimating Corner Frequency and Stress Drop from P-wave Spectra

## Abstract

Empirical Green's functions (EGF) are widely applied to correct earthquake spectra for attenuation and other path effects in order to estimate corner frequencies and stress drops, but these source parameter estimates often exhibit poor agreement between different studies. We investigate this issue by analyzing a compact cluster of over 3000 aftershocks of the 1992 Landers earthquake. We apply and compare two different analysis and modeling methods: (1) the spectral decomposition and global EGF fitting approach, and (2) a more traditional EGF method of modeling spectral ratios. We find that spectral decomposition yields event terms that are consistent with stacks of spectral ratios for individual events, but source-parameter estimates nonetheless vary between the methods. The main source of differences comes from the modeling approach used to estimate the EGF. The global EGF-fitting approach suffers from parameter tradeoffs among the absolute stress drop, the stress-drop scaling with moment, and the high-frequency falloff rate, but has the advantage that the relative spectral shapes and stress drops among the different events in the cluster are well-resolved even if their absolute levels are not. The spectral-ratio approach solves for a different EGF for each target event without imposing any constraint on the corner frequency, fmore »

- Authors:

- Univ. of California, San Diego, CA (United States)
- Boston Univ., MA (United States)
- Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

- Publication Date:

- Research Org.:
- Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

- Sponsoring Org.:
- USDOE National Nuclear Security Administration (NNSA)

- OSTI Identifier:
- 1508559

- Report Number(s):
- LA-UR-18-30681

Journal ID: ISSN 2169-9313

- Grant/Contract Number:
- 89233218CNA000001

- Resource Type:
- Accepted Manuscript

- Journal Name:
- Journal of Geophysical Research. Solid Earth

- Additional Journal Information:
- Journal Name: Journal of Geophysical Research. Solid Earth; Journal ID: ISSN 2169-9313

- Publisher:
- American Geophysical Union

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 58 GEOSCIENCES; GF estimation; corner frequency; stress drop

### Citation Formats

```
Shearer, Peter M., Abercrombie, Rachel E., Trugman, Daniel T., and Wang, Wei. Comparing EGF Methods for Estimating Corner Frequency and Stress Drop from P-wave Spectra. United States: N. p., 2019.
Web. doi:10.1029/2018JB016957.
```

```
Shearer, Peter M., Abercrombie, Rachel E., Trugman, Daniel T., & Wang, Wei. Comparing EGF Methods for Estimating Corner Frequency and Stress Drop from P-wave Spectra. United States. doi:10.1029/2018JB016957.
```

```
Shearer, Peter M., Abercrombie, Rachel E., Trugman, Daniel T., and Wang, Wei. Tue .
"Comparing EGF Methods for Estimating Corner Frequency and Stress Drop from P-wave Spectra". United States. doi:10.1029/2018JB016957.
```

```
@article{osti_1508559,
```

title = {Comparing EGF Methods for Estimating Corner Frequency and Stress Drop from P-wave Spectra},

author = {Shearer, Peter M. and Abercrombie, Rachel E. and Trugman, Daniel T. and Wang, Wei},

abstractNote = {Empirical Green's functions (EGF) are widely applied to correct earthquake spectra for attenuation and other path effects in order to estimate corner frequencies and stress drops, but these source parameter estimates often exhibit poor agreement between different studies. We investigate this issue by analyzing a compact cluster of over 3000 aftershocks of the 1992 Landers earthquake. We apply and compare two different analysis and modeling methods: (1) the spectral decomposition and global EGF fitting approach, and (2) a more traditional EGF method of modeling spectral ratios. We find that spectral decomposition yields event terms that are consistent with stacks of spectral ratios for individual events, but source-parameter estimates nonetheless vary between the methods. The main source of differences comes from the modeling approach used to estimate the EGF. The global EGF-fitting approach suffers from parameter tradeoffs among the absolute stress drop, the stress-drop scaling with moment, and the high-frequency falloff rate, but has the advantage that the relative spectral shapes and stress drops among the different events in the cluster are well-resolved even if their absolute levels are not. The spectral-ratio approach solves for a different EGF for each target event without imposing any constraint on the corner frequency, fc, of the smaller events, and so can produce biased results for target-event fc. Placing constraints on the small-event fc improves the performance of the spectral-ratio method and allows the two methods to yield very similar results.},

doi = {10.1029/2018JB016957},

journal = {Journal of Geophysical Research. Solid Earth},

number = ,

volume = ,

place = {United States},

year = {2019},

month = {4}

}