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Revisiting California's past great earthquakes and long-term earthquake rate

Susan E. Hough, Morgan Page, Leah Salditch, Molly M. Gallahue, Madeleine C. Lucas, James S. Neely and Seth Stein
Revisiting California's past great earthquakes and long-term earthquake rate
Bulletin of the Seismological Society of America (December 2020) Pre-Issue Publication


In this study, we revisit the three largest historical earthquakes in California-the 1857 Fort Tejon, 1872 Owens Valley, and 1906 San Francisco earthquakes-to review their published moment magnitudes, and compare their estimated shaking distributions with predictions using modern ground-motion models (GMMs) and ground-motion intensity conversion equations. Currently accepted moment magnitude estimates for the three earthquakes are 7.9, 7.6, and 7.8, respectively. We first consider the extent to which the intensity distributions of all three earthquakes are consistent with a moment magnitude toward the upper end of the estimated range. We then apply a GMM-based method to estimate the magnitudes of large historical earthquakes. The intensity distribution of the 1857 earthquake is too sparse to provide a strong constraint on magnitude. For the 1872 earthquake, consideration of all available constraints suggests that it was a high stress-drop event, with a magnitude on the higher end of the range implied by scaling relationships, that is, higher than moment magnitude 7.6. For the 1906 earthquake, based on our analysis of regional intensities and the detailed intensity distribution in San Francisco, along with other available constraints, we estimate a preferred moment magnitude of 7.9, consistent with the published estimate based on geodetic and instrumental seismic data. These results suggest that, although there can be a tendency for historical earthquake magnitudes to be overestimated, the accepted catalog magnitudes of California's largest historical earthquakes could be too low. Given the uncertainties of the magnitude estimates, the seismic moment release rate between 1850 and 2019 could have been either higher or lower than the average over millennial time scales. It is further not possible to reject the hypothesis that California seismicity is described by an untruncated Gutenberg-Richter distribution with a b-value of 1.0 for moment magnitudes up to 8.0.

ISSN: 0037-1106
EISSN: 1943-3573
Serial Title: Bulletin of the Seismological Society of America
Serial Volume: Pre-Issue Publication
Title: Revisiting California's past great earthquakes and long-term earthquake rate
Affiliation: U. S. Geological Survey, Pasadena, CA, United States
Published: 20201215
Text Language: English
Publisher: Seismological Society of America, Berkeley, CA, United States
References: 49
Accession Number: 2021-013990
Categories: Seismology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables, sketch maps
N32°30'00" - N42°00'00", W124°30'00" - W114°15'00"
Secondary Affiliation: Northwestern University, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2021, American Geosciences Institute. Abstract, Copyright, Seismological Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 2021
Program Name: USGSOPNon-USGS publications with USGS authors
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