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Fault slip associated with the 2 september 2017 M 5.3 Sulphur Peak, Idaho, earthquake and aftershock sequence

Fred F. Pollitz, Charles Wicks, William L. Yeck and James Evans
Fault slip associated with the 2 september 2017 M 5.3 Sulphur Peak, Idaho, earthquake and aftershock sequence
Bulletin of the Seismological Society of America (April 2019) Pre-Issue Publication

Abstract

The 2 September 2017 M 5.3 Sulphur Peak, Idaho, earthquake is one of the largest earthquakes in southern Idaho since the 1983 M 6.9 Borah Peak earthquake. It was followed by a vigorous aftershock sequence for nearly two weeks that included five events above M 4.5. The coseismic and early postseismic deformation was measured with both Interferometric Synthetic Aperture Radar and Global Positioning System (GPS), yielding up to 3 cm subsidence southwest of the mainshock epicenter and horizontal motions of approximately 1 mm at sites approximately 40 km east and west of the epicenter. We derive dislocation models of the net slip during the approximately 14-day swarm from Sentinel 1A interferograms and GPS offsets, allowing for both fault-zone collapse and normal faulting to account for the observed geodetic motions. Slip inversions yield several decimeters of normal slip on one or more normal faults near the mainshock hypocenter. Distributed normal slip on a moderately (55 degrees ) east-dipping fault, normal slip on one or more shallowly west-dipping faults, or a combination thereof explain the data equally well and are difficult to distinguish from one another on the basis of geodetic data alone. Previously mapped regional Sevier-age thrust structures and later normal faults dip westward, suggesting that the sequence reactivated one or more ancient thrust structures with normal slip. If a moderately east-dipping fault accommodated substantial slip, it would imply a nascent fault structure that cuts across the reactivated ancient thrust structures. The inferred geodetic moment of 3.02-4.39X1017 N.m (Mw 5.62-5.73) greatly exceeds the 1.15X1017 N.m (Mw 5.34) seismic moment of the 2 September mainshock, showing that most of the moment release occurred during the aftershock sequence. Up to approximately 0.2 m of fault-zone collapse may have occurred on a shallow west-dipping fault, suggesting possible large-scale expulsion of fluids from the fault zone at depth.


ISSN: 0037-1106
EISSN: 1943-3573
Coden: BSSAAP
Serial Title: Bulletin of the Seismological Society of America
Serial Volume: Pre-Issue Publication
Title: Fault slip associated with the 2 september 2017 M 5.3 Sulphur Peak, Idaho, earthquake and aftershock sequence
Affiliation: U. S. Geological Survey, Menlo Park, CA, United States
Published: 20190423
Text Language: English
Publisher: Seismological Society of America, Berkeley, CA, United States
References: 31
Accession Number: 2019-037998
Categories: Seismology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sect., 3 tables, sketch maps
N42°30'00" - N43°00'00", W111°49'60" - W111°00'00"
Secondary Affiliation: Utah State University, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Abstract, Copyright, Seismological Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 2019
Program Name: USGSOPNon-USGS publications with USGS authors
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