Tectonic and Environmental Influences on Crustal Deformation in the Western US
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Authors
Miller, Nina
Issue Date
2025
Type
Dissertation
Language
en_US
Keywords
Crustal Deformation , Elastic Dislocation , GPS Geodesy , Seasonal Deformation , Surface Mass Loading , Western United States
Alternative Title
Abstract
This dissertation studies crustal deformation in the western United States using secular and seasonal components of high-precision GPS geodesy. The western U.S. is a zone of active deformation with diverse geological and climatic characteristics, covered by a dense network of GPS stations. It serves as an ideal natural laboratory to address a variety of fundamental questions on fault mechanics, deep magmatic intrusions, as well as the interaction of the environment with the solid earth. The first chapter examines the secular part of the signal in the Walker Lane, a zone of transtensional shear along the west margin of the Basin and Range. A comparison of two competing fault models reveals a profound lack of evidence that locked faults accumulate strain across their surface expressions. Instead, horizontal velocities show uniformly linear deformation, demonstrating that the geodetically observed deformation reflects distributed shear below the brittle crust rather than discrete fault dislocations. This has major implications for seismic hazard assessment, which relies on geodetic strain accumulation rates to estimate earthquake potential on individual faults.The second chapter examines the seasonal part of the GPS signal to demonstrate that hydrologically driven seasonal crustal strain modulates the timing of deep dike openings. The study analyzes all three known deep magmatic intrusions in the western U.S. and finds that each is optimally oriented to receive seasonal reduction in normal stress from hydrological loading, helping the magma to overcome the host rock's resistance and move through the lower crust. Stress reductions of less than 1 kPa are sufficient to facilitate dike opening, demonstrating the sensitivity of deep crustal processes to small environmental stress changes.
The third chapter dissects the seasonal GPS signal in the western U.S. with special attention to the arid Basin and Range. The study describes spatial characteristics of various sources of seasonal elastic deformation and quantifies the relative contributions of the two largest environmental loading sources. Results show that after correcting for global and regional elastic loading signals, the residual deformation adequately captures local hydrological variations. The last two chapters demonstrate coupling between the solid Earth and the hydrosphere and atmosphere, showing that hydrological forcing is significant in the western U.S., even in arid regions, and that weather and climate can affect processes 30 km underground.