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Relaxing segmentation on the Wasatch fault zone; impact on seismic hazard

Alessandro Valentini, Christopher B. DuRoss, Edward H. Field, Ryan D. Gold, Richard W. Briggs, Francesco Visini and Bruno Pace
Relaxing segmentation on the Wasatch fault zone; impact on seismic hazard
Bulletin of the Seismological Society of America (November 2019) 110 (1): 83-109


The multisegment Wasatch fault zone is a well-studied normal fault in the western United States that has paleoseismic evidence of recurrent Holocene surface-faulting earthquakes. Along the 270 km long central part of the fault, four primary structural complexities provide possible along-strike limits to these ruptures and form the basis for models of fault segmentation. Here, we assess the impact that the Wasatch fault segmentation model has on seismic hazard by evaluating the time-independent long-term rate of ruptures on the fault that satisfy fault-slip rates and paleoseismic event rates, adapting standard inverse theory used in the Uniform California Earthquake Rupture Forecast, Version 3, and implementing a segmentation constraint in which ruptures across primary structural complexities are penalized. We define three models with varying degrees of rupture penalization: (1) segmented (ruptures confined to individual segments), (2) penalized (multisegment ruptures allowed, but penalized), and (3) unsegmented (all ruptures allowed). Seismic-hazard results show that, on average, hazard is highest for the segmented model, in which seismic moment is accommodated by frequent moderate (moment magnitude Mw 6.2-6.8) earthquakes. The unsegmented model yields the lowest average seismic hazard because part of the seismic moment is accommodated by large (Mw 6.9-7.9) but infrequent ruptures. We compare these results to model differences derived from other inputs such as slip rate and magnitude scaling relations and conclude that segmentation exerts a primary control on seismic hazard. This study demonstrates the need for additional geologic constraints on rupture extent and methods by which these observations can be included in hazard-modeling efforts.

ISSN: 0037-1106
EISSN: 1943-3573
Serial Title: Bulletin of the Seismological Society of America
Serial Volume: 110
Serial Issue: 1
Title: Relaxing segmentation on the Wasatch fault zone; impact on seismic hazard
Affiliation: Universita "G. d'Annunzio" di Chieti-Pescara, Chieti, Italy
Pages: 83-109
Published: 20191119
Text Language: English
Publisher: Seismological Society of America, Berkeley, CA, United States
References: 60
Accession Number: 2020-002475
Categories: Seismology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: Includes appendices
Illustration Description: illus. incl. 5 tables, sketch maps
N40°00'00" - N41°30'00", W112°00'00" - W111°30'00"
Secondary Affiliation: U. S. Geological Survey, USA, United StatesIstituto Nazionale di Geofisica e Vulcanologia, ITA, Italy
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2020, American Geosciences Institute. Abstract, Copyright, Seismological Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 202003
Program Name: USGSOPNon-USGS publications with USGS authors
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