Title: 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, f_c,more » of the smaller events, and so can produce biased results for target-event f_c. Placing constraints on the small-event f_c improves the performance of the spectral-ratio method and allows the two methods to yield very similar results.« less

Authors:

Shearer, Peter M.  ^[1];

• Search DOE PAGES for author "Shearer, Peter M."
• Search DOE PAGES for ORCID "0000-0002-2992-7630"

Abercrombie, Rachel E.  ^[2];

• Search DOE PAGES for author "Abercrombie, Rachel E."
• Search DOE PAGES for ORCID "0000-0003-4515-5420"

Trugman, Daniel T.  ^[3];

• Search DOE PAGES for author "Trugman, Daniel T."
• Search DOE PAGES for ORCID "0000-0002-9296-4223"

Wang, Wei ^[1]

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+ Show Author Affiliations

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

Publication Date:

Tue Apr 02 00:00:00 EDT 2019

Research Org.:

Los Alamos National Laboratory (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 Volume: 124; Journal Issue: 4; 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