Document Type

Thesis

Date of Degree Completion

Spring 2025

Degree Name

Master of Science (MS)

Department

Geological Sciences

Committee Chair

Timothy Melbourne

Second Committee Member

Walter Szleiga

Third Committee Member

Craig Scrivner

Abstract

Non-volcanic tremor, a low-amplitude, 1-5 Hz long-duration seismic noise signal easily resolvable by short-period seismometers of the Pacific Northwest Seismic Network, is the canonical seismic signature observed during Cascadia Episodic Tremor and Slip (ETS) Events. Whether significant energy is released at periods longer than 1 Hz has not been systematically searched for but nonetheless may exist and if so, could represent both a significant portion of the Cascadia moment budget as well as a mechanism by which slow slip and regular seismicity interact. The August 2010 ETS event beneath Puget Sound was well-recorded by a wide range of instruments that allows for both a detailed study of this ETS event as well as constraints on any long-period moment release, should it exist, including the PNSN, PANGA, long-baseline tiltmeters, borehole-strainmeters, and a specifically-installed broadband seismic array, the “Sequim Valley Seismic Array (SVSA), installed to measure long-period moment release. The seismic data was cut into 24-hour files and then the instrument response was removed. Data was then searched for long period moment release using a filtering method to look for very low frequency earthquakes (VLFE) signals. The analysis of the SVSA data showed that the array was coupled with the Earth as good records of long period energy from teleseisms was recorded. But the by-hand analysis using filtering methods did not show any evidence of VLFES or other long period signals. From this we conclude that the moment budget for slow slip does not include significant energy at frequencies lower than the well-established tremor band between 1-8 Hz, as visible without advanced array analysis techniques.

Download

Share

COinS