Williams, JR, Hawthorne, JC, Rost, S orcid.org/0000-0003-0218-247X et al. (1 more author) (2019) Stress Drops on the Blanco Oceanic Transform Fault from Interstation Phase Coherence. Bulletin of the Seismological Society of America, 109 (3). pp. 929-943. ISSN 0037-1106
Abstract
Oceanic transform faults display a wide range of earthquake stress drops, large aseismic slip, and along‐strike variation in seismic coupling. We use and further develop a phase coherence‐based method to calculate and analyze stress drops of 61 M≥5.0 events between 2000 and 2016 on the Blanco fault, off the coast of Oregon. With this method, we estimate earthquake rupture extents by examining how apparent source time functions (ASTFs) vary between stations. The variation is caused by the generation of seismic waves at different locations along the rupture, which arrive at different times depending on station location. We isolate ASTFs at a range of stations by comparing seismograms of collocated earthquakes and then use the interstation ASTF coherence to infer rupture extent and stress drop.
We examine how our analysis is influenced by various factors, including poor trace alignment, relative earthquake locations, focal mechanism variation, azimuthal distribution of stations, and depth phase arrivals. We find that as alignment accuracy decreases or distance between earthquakes increases, coherence is reduced, but coherence is unaffected by focal mechanism variation or depth phase arrivals for our dataset. We calibrate the coherence–rupture extent relationship based on the azimuthal distribution of stations.
We find the phase coherence method can be used to estimate stress drops for offshore earthquakes, but is limited to M≥5.0 earthquakes for the Blanco fault due to poor trace alignment accuracy. The median stress drop on the Blanco fault is 8 MPa (with 95% confidence limits of 6–12 MPa) for 61 earthquakes. Stress drops are a factor of 1.7 (95% confidence limits 0.8–3.5) lower on the more aseismic northwest segment of the Blanco fault. These lower stress drops could be linked to reduced healing time due to higher temperatures, which reduce the depth of the seismogenic zone and shorten the seismic cycle.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © Seismological Society of America. This is an author produced version of an article published in Bulletin of the Seismological Society of America. Uploaded in accordance with the publisher's self-archiving policy. |
Keywords: | earthquakes; stress drops; blanco fault; strike-slip; properties |
Dates: |
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Institution: | The University of Leeds |
Academic Units: | The University of Leeds > Faculty of Environment (Leeds) > School of Earth and Environment (Leeds) > Inst of Geophysics and Tectonics (IGT) (Leeds) |
Funding Information: | Funder Grant number NERC No External Reference NERC NE/I028017/1 |
Depositing User: | Symplectic Publications |
Date Deposited: | 30 Apr 2019 11:53 |
Last Modified: | 07 Nov 2019 01:39 |
Status: | Published |
Publisher: | Seismological Society of America |
Identification Number: | 10.1785/0120180319 |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:145490 |