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Contributions to the Neotectonics of the central and northern Walker Lane
AdvisorWesnousky, Steven G
Geological Sciences and Engineering
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The Walker Lane is a well-known intraplate shear zone located east of the Sierra Nevada that accommodates a significant portion of the North American – Pacific Plate relative transform motion. It its defined by a broad zone of discontinuous active strike-slip and normal faulting that sit within a zone geodetically characterized by transtensional dextral shear. Strain in the Walker Lane is driven by the northwest translation of the Sierra Nevada and long-term geologic constraints on the distribution and partitioning of slip amongst the active faults are limited, thus our understanding of how these faults interact and behave as a system remains understudied. These limitations are a consequences of the slow-slip rate environments, making geomorphic preservation and observation of offset more difficult, and due to the state of scientific advancement. Similarly, at the northern end of the Sierra Nevada, regional north-south oriented contraction is geodetically observed and has been attributed to the interaction of the northwest translating Sierra Nevada with the overriding crust of the southern Cascadia Subduction Zone. Accommodation of this strain remains geologically unaccounted for, thus it is unknown how the contraction is accommodated. The purpose of this dissertation is to place new and more robust constraints on the rates of slip for multiple Walker Lane faults and to identify and characterize potentially active faults within the northern Sierra and southern Cascadia transition zone. Much of this work is motivated by seismic hazard, but scientifically serves to provide a better understanding of how strain is released bordering the Sierra Nevada Mountains. This dissertation consists of 3 chapters. The first study explores a new application of a ground surface modeling technique for the purpose of placing better constraints on the rate of slip for the Pyramid Lake fault, a major strike-slip fault in the northern portion of the Walker Lane. This study is herein presented as published in the Bulletin of the Seismological Society of America (Vol. 106, No. 2, 2016). Chapter 2 builds on this method and incorporates multiple Quaternary dating techniques that place constraints on horizontal slip-rates in a network of strike-slip faults that comprise the central Walker Lane. The observations and new rates obtained in this study provide insight into how slip is accommodated on a variety of spatiotemporal scales. Finally, chapter 3 presents the results from a combination of geophysical, geologic, and geomorphic observations made within the northern Sacramento Valley that show the presence of Quaternary contractional deformation associated with a series of previously identified structures optimally oriented to accommodate north-south contraction. These findings show for the first time, how geodetically observed strain is accommodated within the northern Sierra and southern Cascadia transition zone.