Document Type

Thesis

Date of Degree Completion

Fall 2025

Degree Name

Master of Science (MS)

Department

Geological Sciences

Committee Chair

Breanyn MacInnes

Second Committee Member

Lisa Ely

Third Committee Member

Walter Szeliga

Abstract

This study uses GeoClaw to simulate 8 instantaneous rupture test earthquakes and 48 stochastic earthquakes (Fakequakes) along the Cascadia Subduction Zone to better understand tsunami generation and propagation. The primary goal is to evaluate how variations in Fakequake rupture patterns affect tsunami heights at coastal sites in the Pacific Northwest. The study focused on comparing inner and outer coast wave heights and impacts to understand how the Olympic Peninsula provides a barrier of protection to inner coast sites from southern-generated tsunamis, and implications for tsunami hazard at Naval Air Station Whidbey Island (NASWI).

Test earthquakes show increased amounts of slip with varying earthquake magnitudes lead to increased amounts of positive displacement, which produces larger wave heights than having a set magnitude and variable slip. The displacement concentration of Fakequakes directly influences both the wave height and spatial pattern of tsunamis. Fakequakes with high amounts of displacement offshore from, or near, a gauge site generally created higher wave heights at that site while sites farther away from the peak displacement concentrations often experienced smaller wave heights. The Olympic Peninsula generally prevents large wave heights in the Salish Sea from southern-rupture scenarios. When Fakequake inundation at gauge sites was compared to observed paleotsunami evidence, few Fakequakes were found to be a strong match for future comparison. Only four of the 48 Fakequakes inundated at NASWI, suggesting that NASWI is generally not vulnerable to tsunamis except in certain severe earthquake scenarios.

These findings highlight the importance of using multiple rupture scenarios in tsunami hazard assessments rather than relying on a single model. Additionally, paleotsunami records can be difficult to match to simulated scenarios unless a margin of error in matching the sites is introduced. This research suggests that slip distribution patterns are key to understanding tsunami hazard risk at coastal sites, and should be a major consideration in emergency planning, risk mapping, and coastal hazard mitigation strategies.

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