Effects of internal fault zone properties on seismic imaging
Abstract
The objective of this fault zone study was to examine the relationship between internal fault zone properties and seismic images, using detailed laboratory analysis and modeled seismic responses. Three classic fault zones, the San Andreas, Brevard and Outer Hebrides Thrust, where studied, representing a diverse range of fault zone geometries, rocks, and seismic images. Laboratory analyses of the rock samples collected to represent the fault zones and their surrounding geology, included: petrographic descriptions, whole rock chemical analyses, measurement of compressional and shear wave velocities, densities, seismic anisotropies, and Poisson's ratios. The individual fault zone studies each provided important interpretations of fault zone structures and properties. The study of the San Andreas fault in Southern California lead to an interpretation of crustal composition and structure surrounding the fault zone by correlating measured seismic properties with seismic field data. Detailed analysis of the shear wave properties in the Brevard fault zone, North Carolina, illustrated the ability of shear wave studies to enhance traditional compressional wave interpretation of fault zone composition and structure. Measuring the seismic properties of rocks representing a brittle-ductile transition in a fault zone, the Outer Hebrides Thrust, provided a critical link between the properties observed in brittle and ductile faults. Combining the individual fault zone results produced additional conclusions regarding fault zone properties and seismic imaging. First, the diverse geologic setting surrounding fault zones generate a wide range of fault zones rocks, compositions and seismic properties. Second, seismic properties in a fault zone are directly related to mineral composition, where seismic velocities increase with a progressive change from quartz and feldspars to amphiboles and pyroxenes. Third, determining shear wave images and properties enhance our understanding of fault zone structure and highlight possible regions of high pore pressure. Fourth, seismic anisotropy affects seismic imaging in various ways, such as enhancing reflectivity or complicating crustal velocity structure. Thus, anisotropy must be carefully considered when interpreting seismic images. Finally, the complexities of the brittle-ductile transition in fault zones make it difficult to correlate deformation and seismic properties.
Degree
Ph.D.
Advisors
Christensen, Purdue University.
Subject Area
Geophysics
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