Electronic Theses and Dissertations

Date

2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Earth Sciences

Committee Chair

Chris Cramer

Committee Member

Eunseo Choi

Committee Member

Thomas Goebel

Committee Member

Christodoulos Kyriakopoulos

Committee Member

Shahram Pezeshk

Abstract

This study synthesizes findings from a comprehensive seismic attenuation investigation across Alaska, employing data from the EarthScope USArray spanning 2014 to 2020. The analysis integrates crustal seismic (Q_Lg^(-1)) attenuation mapping with an examination of intrinsic (Q_s^(-1)) and scattering (Q_i^(-1)) attenuation contribution on total seismic wave attenuation. By employing the Multiple Lapse Time Window Analysis (MLTWA) and focusing on earthquakes with magnitudes ranging from 2.0 to 6.5, this research delineates the complex interplay of geological structures with seismic wave attenuation behavior, offering significant insights for regional seismic hazard assessments. The crustal seismic (Q_Lg^(-1)) attenuation component of the study reveals significant variations in Q_Lg^(-1) values across Alaska, with the lowest attenuation found in regions with tectonic terranes such as the Yukon–Tanana and Togiak Terranes. Higher attenuation levels were observed in the southeast near the Wrangell Volcanoes and along the major fault systems, including the Denali and Castle Mountain faults. These findings suggest that both the geological composition and the tectonic dynamics of these regions play a crucial role in influencing seismic wave attenuation patterns. The notably higher average Q_Lg values in Alaska, compared to the western U.S. and Canada, highlight the unique seismic characteristics of the region, influencing local seismic hazard predictions and the expected intensity of seismic activity. In the study focusing on intrinsic and scattering attenuation, pronounced spatial variations in scattering loss were observed, particularly significant at frequencies up to 3 Hz, which diminish at higher frequencies like 6 and 12 Hz. The area north of the Alaska Range exhibited marked scattering loss, with the highest intrinsic absorption rates detected at specific frequencies, underscoring the diverse absorption characteristics across different regions. The seismic albedo (B_0) varied significantly, indicating that both scattering and intrinsic mechanisms contribute to the overall attenuation, with regions like the Chugach Mountains and Yakutat block showing dominance in intrinsic absorption. These results provide a detailed understanding of the attenuation processes, essential for advancing seismic wave analysis and enhancing the accuracy of seismic hazard models in Alaska.

Comments

Data is provided by the student.

Library Comment

Dissertation or thesis originally submitted to ProQuest.

Notes

Open Access

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