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Date of Award

Spring 2024

Document Type

Masters Thesis

Department or Program Affiliation

Geology

Degree Name

Master of Science (MS)

Department

Geology

First Advisor

Roland, Emily Carlson

Second Advisor

Boettcher, Margaret S.

Third Advisor

Caplan-Auerbach, Jacqueline

Fourth Advisor

Amos, Colin B.

Abstract

The Gofar oceanic transform fault (OTF) accommodates 12.5 cm/year of plate boundary motion through large earthquakes, microseismic swarms, and aseismic slip in distinct regions of the fault along strike. Local and teleseismic observations show that well- coupled segments of the fault tend to fail via M~6 earthquakes roughly every 5 years. These fully-coupled segments are bound by barrier zones, up to ~10 km-wide, that do not generate large-magnitude earthquakes, but instead host microseismic swarms, accompanied by aseismic slip (Shi et al., 2021). Geophysical modeling and observations provide evidence that hydrothermal fluid circulation and fault damage may influence slip behavior segmentation. Here I present the fine-scale surface morphology of the Gofar OTF as characterized by 1-meter-resolution autonomous underwater vehicle (AUV) multibeam bathymetry. These data reveal a complex fault system, with variations in fault strike, fault bends, sub-parallel strands, and a heterogenous damage zone of variable width. The scale of fault complexity shown through the AUV- determined micro-bathymetry is not previously imaged with ship-based bathymetry (> 50 m resolution) and provides significant new insight into how surface fault morphology changes along strike. Newly mapped fault structural variation partially correlates with the along-strike rupture segmentation from local seismic observations, reflecting a possible change in material or structural fault properties related to changes in fault rheology and mechanisms of fault slip. Using new high-resolution information on surface morphology, we find that regions that sustain repeated, high magnitude ruptures are expressed as a relatively linear principal slip zones (PSZ) striking in a similar direction to global plate motions contained within a relatively thin (≤ ~ 500 m) margin of damage. In contrast, regions that contain deep microseismicity and no high magnitude rupture are geomorphically complex, with changes to PSZ orientation within a relatively wide (≥ 500 m) region of damage. These observations imply that at Gofar, geometric bends in fault strike are also associated with a widened zone of subsidiary faulting and distributed fractures which could facilitate enhanced fluid flow, allowing more water to extend through the seismogenic zone, subsequently altering the material properties that contribute to slow slip.

Type

Text

Keywords

multibeam bathymetry, oceanic transform fault, Gofar, Sentry AUV

Publisher

Western Washington University

OCLC Number

1439128973

Subject – LCSH

Multibeam mapping--East Pacific Rise; Fault zones--East Pacific Rise; Strike-slip faults (Geology)--East Pacific Rise; Surface fault ruptures--East Pacific Rise; Earthquake zones--East Pacific Rise; Mid-ocean ridges--Pacific Ocean; Autonomous underwater vehicles

Geographic Coverage

East Pacific Rise; Pacific Ocean

Format

application/pdf

Genre/Form

masters theses

Language

English

Rights

Copying of this document in whole or in part is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this document for commercial purposes, or for financial gain, shall not be allowed without the author’s written permission.

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