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This content will become publicly available on March 6, 2019

Title: Strong correlation between stress drop and peak ground acceleration for recent M1–4 earthquakes in the San Francisco Bay Area

Theoretical and observational studies suggest that between-event variability in the median ground motions of larger ( M≥5 ) earthquakes is controlled primarily by the dynamic properties of the earthquake source, such as Brune-type stress drop. Analogous results remain equivocal for smaller events due to the lack of comprehensive and overlapping ground-motion and source-parameter datasets in this regime. Here in this paper, we investigate the relationship between peak ground acceleration (PGA) and dynamic stress drop for a new dataset of 5297 earthquakes that occurred in the San Francisco Bay area from 2002 through 2016. For each event, we measure PGA on horizontal-component channels of stations within 100 km and estimate stress drop from P-wave spectra recorded on vertical-component channels of the same stations. We then develop a nonparametric ground-motion prediction equation (GMPE) applicable for the moderate (M 1–4) earthquakes in our study region, using a mixed-effects generalization of the Random Forest algorithm. We use the Random Forest GMPE to model the joint influence of magnitude, distance, and near-site effects on observed PGA. We observe a strong correlation between dynamic stress drop and the residual PGA of each event, with the events with higher-than-expected PGA associated with higher values of stress drop.more » The strength of this correlation increases as a function of magnitude but remains significant even for smaller magnitude events with corner frequencies that approach the observable bandwidth of the acceleration records. Mainshock events are characterized by systematically higher stress drop and PGA than aftershocks of equivalent magnitude. Coherent local variations in the distribution of dynamic stress drop provide observational constraints to support the future development of nonergodic GMPEs that account for variations in median stress drop at different source locations.« less
Authors:
ORCiD logo [1] ;  [2]
  1. Univ. of California, San Diego, CA (United States). Scripps Inst. of Oceanography, Inst. of Geophysics and Planetary Physics; Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  2. Univ. of California, San Diego, CA (United States). Scripps Inst. of Oceanography, Inst. of Geophysics and Planetary Physics
Publication Date:
Report Number(s):
LA-UR-18-20708
Journal ID: ISSN 0037-1106 ; 1943-3573 (Electronic)
Grant/Contract Number:
AC52-06NA25396; DGE-1144086; 16020
Type:
Accepted Manuscript
Journal Name:
Bulletin of the Seismological Society of America
Additional Journal Information:
Journal Volume: 108; Journal Issue: 2; Journal ID: ISSN 0037-1106
Publisher:
Seismological Society of America
Research Org:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org:
National Science Foundation (NSF); USDOE
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES
OSTI Identifier:
1430024