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Earthquake interaction, fault structure, and source properties of a small sequence in 2017 near Truckee, California

Rachel L. Hatch, Rachel E. Abercrombie, Christine J. Ruhl and Kenneth D. Smith
Earthquake interaction, fault structure, and source properties of a small sequence in 2017 near Truckee, California
Bulletin of the Seismological Society of America (October 2018) 108 (5A): 2580-2593

Abstract

We use relocation and source parameter analysis, including stress drop and directivity, to investigate fault structure and earthquake interaction of small-magnitude earthquakes within a sequence in the Walker Lane tectonic region. Two high-angle, left-lateral strike-slip earthquakes (Mw 3.65 foreshock and Mw 3.85 mainshock), occurred 7 min apart, approximately 20 km north of Truckee, California, on 27 June 2017. Both events were felt over a wide area in northeastern California and northwestern Nevada and happened nearby Holocene fault zones including the Polaris, Mohawk Valley, and Dog Valley Quaternary fault zones that pose a significant hazard to the populated regions in the area. We use waveform cross correlation to relocate the earthquakes and empirical Green's-function methods to estimate the source parameters of all ML>2 events. Also, we estimate the rupture directivity for the two largest events. We relocate 50 out of 52 earthquakes within the sequence, with an average relative error of <30 m. The events define a single structure between 5 and 6 km depth, trending approximately N45 degrees E and dipping approximately 70 degrees -80 degrees to the northwest. The distribution of relocations matches the northeast-striking plane from both the moment tensor solutions and computed first-motion focal mechanisms, indicating sinistral strike-slip motion on a previously unmapped fault. We observe average stress drops of approximately 5 MPa using P and S waves and spatial variation related to the rupture areas of the foreshock and mainshock. We are able to detect components of directivity toward the northeast for the foreshock (Mw 3.65) and directivity toward the southwest for the mainshock (Mw 3.85), both aligning with the fault plane. This analysis illustrates details in source properties and rupture propagation that can be derived with high-precision event locations within dense regional networks and provides more data and a better understanding as it relates to potential seismic hazard.


ISSN: 0037-1106
EISSN: 1943-3573
Coden: BSSAAP
Serial Title: Bulletin of the Seismological Society of America
Serial Volume: 108
Serial Issue: 5A
Title: Earthquake interaction, fault structure, and source properties of a small sequence in 2017 near Truckee, California
Affiliation: University of Nevada at Reno, Reno, NV, United States
Pages: 2580-2593
Published: 201810
Text Language: English
Publisher: Seismological Society of America, Berkeley, CA, United States
References: 83
Accession Number: 2018-084074
Categories: Seismology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table, sketch maps
N38°47'60" - N39°36'00", W120°24'00" - W119°35'60"
Secondary Affiliation: Boston University, USA, United StatesUniversity of California at Berkeley, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute. Abstract, Copyright, Seismological Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201821
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