Date of Award

8-14-2024

Author's School

Graduate School of Arts and Sciences

Author's Department

Earth & Planetary Sciences

Degree Name

Doctor of Philosophy (PhD)

Degree Type

Dissertation

Abstract

This dissertation utilizes multiple techniques of seismic tomography to investigate the crust and uppermost mantle structure of two prominent convergent margins: the Alaska and Mariana subduction zones. The study of the Alaska subduction zone largely benefits from the Alaska Amphibious Community Seismic Experiment (AACSE) that deployed from May 2018 to September 2019, as well as the EarthScope Transportable Array (TA) that was simultaneously operating across Alaska. Using 271 seismic stations in total, I analyze the Rayleigh wave phase and group velocity dispersion data retrieved from both ambient noise and teleseismic earthquake data. I then determine the shear velocity model by jointly inverting the local Rayleigh wave dispersion (phase velocity from 8 to 100 s and group velocity from 8 to 36 s) and station-based receiver functions. The shear velocity structure reveals the along-strike variations in the incoming plate hydration, forearc crustal thickness, and backarc structure. The water input into the Shumagin segment is about twice that in the Semidi segment, suggesting the requirements of detailed imaging in estimating the total water flux through the trench. The azimuthal anisotropy analysis reveals the consistent along-strike variation pattern and provides more confidence that the velocity reduction at the top of the mantle is caused by mantle serpentinization. The study of the Mariana subduction zone uses the ocean bottom seismic data of a Mariana temporary experiment deployed from January 2012 to February 2013. The motivation is to improve the earlier shear velocity structure that was determined using only the fundamental Rayleigh waves. The inclusion of fundamental mode Love waves and first-overtone Rayleigh waves greatly helps resolve the shallow structure due to their reduced sensitivity to ocean depth. A preliminary shear velocity structure is determined using only fundamental Love and Rayleigh waves and assuming no anisotropy. The updated model is similar to the previous shear velocity structure, but shows little velocity reduction in the incoming plate at distances greater than 100 km from the trench. The velocity reduction beneath the Moho near the trench is also somewhat less than in the previous model. The results still support the previous estimate of water flux into the subduction zone, but indicate additional datasets besides the fundamental mode Rayleigh wave are important to determine the accurate oceanic crustal and uppermost mantle structure.

Language

English (en)

Chair and Committee

Douglas Wiens

Committee Members

Michael Wysession; Philip Skemer; V. Slava Solomatov; Weisen Shen

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