Date of Award

2019-01-01

Degree Name

Master of Science

Department

Geophysics

Advisor(s)

Aaron A. Velasco

Abstract

Understanding the stress state of faults and the stress needed to trigger earthquakes remains a fundamental goal for understanding the earthquake cycle. We focus on deciphering the stress of faults by studying seismic waves from large, distant earthquakes that trigger local seismicity, called remote or dynamic triggering. Utilizing 17 years of waveform and catalog data (2000-2017) from seismic regional networks (i.e., EarthScope USArray Transportable Array, United States Geological Survey, and University of Utah Regional networks), we search for triggered seismicity in the state of Utah following 227 large magnitude (M ≥ 7) distant earthquakes. Utah provides a long-standing regional network that has a low magnitude threshold that allows for the analysis of small, triggered events. We apply three distinct approaches: 1) a catalog analysis with a statistical approach, 2) an automatic detection analysis using similar statistics, and 3) a visual inspection of events. Using the UUSS seismic catalog, we identify increased seismicity rates after the passage the transient seismic waves for only 5 large magnitude earthquakes that show potential remote triggering in Utah. For our automated detection analysis, we apply a short term to long term detector to high-pass (5 Hz) across filtered ± 5 hours of waveform data after the origin time of each event for 101 seismic stations to identify potentially remotely triggered earthquakes. We build upon previously developed automated methods and find that 89 M ≥ 7 earthquakes show potential for triggered seismicity. During the visual inspection, we identify previous uncatalogued small, local earthquakes associated with 65 mainshock earthquakes. Of these 65 mainshock earthquakes, 18 display an increase in seismicity indicative of dynamic triggering. Comparing our three analyses, we find our modified automated method is suitable for highlighting areas prone to dynamic triggering. A comparison of the catalog and visually detection analysis revealed that a majority of the local events (including triggered) are absent from the catalog data. We hypothesize that this discrepancy is due to these local events having lower magnitudes than those included in the catalog. We also find that most surface waves approach the regional faults perpendicular to strike. We hypothesize that due to the strain experienced during the passage of the surface waves the faults experience an instance of decoupling.

Language

en

Provenance

Received from ProQuest

File Size

41 pages

File Format

application/pdf

Rights Holder

David Lewis Guenaga

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