Title

Magnetic Properties of the Bishop Ash in the San Andreas Fault Borderlands

Degree Year

2011

Document Type

Thesis

Degree Name

Bachelor of Arts

Department

Geology

Abstract

The San Andreas Fault marks one of the most tectonically active regions of the United States, producing frequent earthquakes that have decimated major population centers throughout central and southern California. Its northern regions have been thoroughly studied, but the complex behavior of the southeast portion of the fault is often neglected, in spite of its potential to nucleate a major earthquake within the next few centuries. In this study, I examined the magnetic traits of the Bishop Ash, a well-dated marker horizon of volcanic ash, to assess deformation adjacent to this part of the fault at hand-sample scale. To this end, I first characterized the magnetic properties of the Ash and found that while magnetite is present in small concentrations, the anisotropy of magnetic susceptibility (AMS) is controlled by the crystallographic fabric of paramagnetic minerals. The scatter of anisotropy axes implies that individual grains may have been slightly reoriented during deformation. I also attempted to use magnetic remanence to determine whether significant vertical axis reorientation has occurred since initial deposition; however, the recorded remanence is likely a chemical remanent magnetization (CRM) acquired after deposition.

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