A High-Resolution Seismic Reflection and Gravity Survey of Quaternary Deformation Across the Wasatch Fault, Utah

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High-resolution reflection seismic and detailed gravity data were acquired across an exposure of the Wasatch fault, Utah, near a trench excavated for dating of Quaternary fault displacement. The seismic data across the Quaternary Wasatch fault are interpreted to show three subparallel surfaces dipping from 70°W at the surface to an estimated 45°W at 40 m, displaced unconsolidated sediments, and colluvial material abutting the main fault. Detailed gravity data were of assistance in mapping the sediment-bedrock interface from the rangefront across the Wasatch Fault Zone. A combined high-resolution seismic and gravity interpretation reveals that bedrock is 80 m deeper in the hanging wall than in the footwall, suggesting that displacement has occurred on several en echelon blocks in the near-surface of the Wasatch fault. Movement on the most recent Wasatch fault trace began prior to deposition of Pleistocene lacustrine sediments. The twelvefold, high-resolution reflection seismic data were recorded and processed to achieve vertical resolution of approximately 1 m and horizontal resolution (Fresnel zone radii) of as good as 5 m on the deepest reflecting interfaces at 40 m. Reasonably high frequencies and good bandwidth (about 80–300 Hz) in the stacked seismic data permitted a direct comparison to the trenched cross section. Good correlation between the trench stratigraphy and structure and the seismic data suggests high-resolution seismic data can be a valuable tool for analyzing near-surface faulting in unconsolidated sediment and for locating potential trench sites.

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An edited version of this paper was published by AGU. Copyright 1993 American Geophysical Union. DOI: 10.1029/92JB02873