The vast majority of theses in this collection are open access and freely available. There are a small number of theses that have access restricted to the WWU campus. For off-campus access to a thesis labeled "Campus Only Access," please log in here with your WWU universal ID, or talk to your librarian about requesting the restricted thesis through interlibrary loan.

Date of Award

Summer 2025

Document Type

Masters Thesis

Department or Program Affiliation

Geology

Degree Name

Master of Science (MS)

Department

Geology

First Advisor

Roland, Emily Carlson

Second Advisor

DeBari, Susan M., 1962-

Third Advisor

Worthington, Lindsay

Abstract

The Queen Charlotte Fault (QCF) accommodates right-lateral transform motion between the Pacific and North American plates offshore southeast Alaska and British Columbia, generating Mw>7 earthquakes every few decades. Despite its being the longest and fastest-slipping ocean-continent transform boundary on Earth, physical controls on earthquake behavior and deformation along the QCF remain poorly understood due to the fault’s remote offshore setting. Recent bathymetric mapping reveals several fault step-overs associated with localized zones of compression and extension that often coincide with earthquake rupture terminations, suggesting they may act as barriers to slip. Some step-overs also lie adjacent to active volcanic fields, raising questions about their role in melt transport and regional magmatism. Here, I use streamer-recorded wide-angle refraction data from the 2021 Transform Obliquity along the Queen Charlotte and Earthquake Study (TOQUES) experiment to construct a P-wave velocity model along a ~340 km transect on the North American plate parallel to the QCF. I focus on the structure of the continental shelf, including regions adjacent to three fault step-overs, with the goals of characterizing the distribution of sediment and bedrock adjacent to the fault, and searching for signs of previously undiscovered young volcanic activity. The final velocity model reveals a two-layer crust, with low-velocity sediments overlying high-velocity basement, and shows no evidence of low velocity anomalies consistent with melt. Shallow high-velocity anomalies align spatially with the step-overs, indicating a potential structural control on fault segmentation. I interpret these anomalies as solidified intermediate to mafic plutons, likely formed in a submarine volcanic arc and later accreted to the margin. These findings are supported by complementary marine geophysical datasets, and suggest that pre-existing lithologic heterogeneity influences both QCF geometry and earthquake behavior.

Type

Text

Keywords

Queen Charlotte Fault, seismic velocity, streamer, tomography, crustal structure, seismic refraction

Publisher

Western Washington University

OCLC Number

1527215101

Subject – LCSH

Surface fault ruptures--Alaska; Surface fault ruptures--British Columbia--Haida Gwaii Region; Faults (Geology)--Alaska; Faults (Geology)--British Columbia--Haida Gwaii Region; Fault zones--Alaska; Fault zones--British Columbia--Haida Gwaii Region; Earthquake zones--Alaska; Earthquake zones--British Columbia--Haida Gwaii Region; Earthquakes--Alaska; Earthquakes--British Columbia--Haida Gwaii Region; Seismic tomography--Alaska; Seismic tomography--British Columbia--Haida Gwaii Region; Seismic waves--Speed--Measurement; Seismic refraction method; Seismic traveltime inversion

Geographic Coverage

Alaska; British Columbia; Haida Gwaii (B.C.)

Format

application/pdf

Genre/Form

masters theses

Language

English

Download

Included in

Geology Commons

Share

COinS