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Improving paleoseismic earthquake magnitude estimates with rupture length information; application to the Puget Lowland, Washington State, U.S.A.

Richard H. Styron and Brian Sherrod
Improving paleoseismic earthquake magnitude estimates with rupture length information; application to the Puget Lowland, Washington State, U.S.A.
Bulletin of the Seismological Society of America (December 2020) 111 (2): 1139-1153

Abstract

Both earthquake displacement and rupture length correlate with magnitude, and, therefore, observations of each from past earthquakes can be used to estimate the magnitude of those earthquakes in the absence of instrumental records. We extend the Bayesian inversion method of Biasi and Weldon (2006), which estimates paleoearthquake magnitude from displacement observations, to incorporate both rupture length and surface displacement measurements into the magnitude inversion. We then use this method on 27 late-Pleistocene to Holocene paleoearthquakes in the Puget Lowland region of Washington. Observations of (typically vertical) fault separation per event range from 0.6 to 7 m, implying net displacement per event of up to 10+ or -4 m for the largest event. Rupture lengths are estimated to vary between the smallest contiguous mapped scarps to the full extent of the faults mapped from geology and geophysical observations. Although, a few of the ruptures may be longer than 150 km, the ruptures have a median of 53 km, indicating that earthquakes in the Puget Lowland have relatively high displacement-to-length ratios. By considering both datasets, we find that all events were between M 6.3 and 7.5, generally consistent with the expected seismicity from the U.S. Geological Survey National Seismic Hazard Map for the region. The simultaneous use of both length and displacement data in the magnitude inversion decreases both the estimated earthquake magnitudes and the uncertainty. The magnitude reduction, in particular, is due to the relatively short rupture lengths possible for Puget Lowland faults. This implies a decrease in the seismic hazard (relative to a displacement-only assessment) to a highly populated and rapidly urbanizing region.


ISSN: 0037-1106
EISSN: 1943-3573
Coden: BSSAAP
Serial Title: Bulletin of the Seismological Society of America
Serial Volume: 111
Serial Issue: 2
Title: Improving paleoseismic earthquake magnitude estimates with rupture length information; application to the Puget Lowland, Washington State, U.S.A.
Affiliation: Earth Analysis, Portland, OR, United States
Pages: 1139-1153
Published: 20201215
Text Language: English
Publisher: Seismological Society of America, Berkeley, CA, United States
References: 68
Accession Number: 2021-013989
Categories: Seismology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables, sketch maps
N47°00'00" - N49°00'00", W125°00'00" - W122°00'00"
Secondary Affiliation: U. S. Geological Survey, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2022, American Geosciences Institute. Abstract, Copyright, Seismological Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 202110
Program Name: USGSOPNon-USGS publications with USGS authors
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