High-Resolution Seismic Imaging and Gravity Analysis of Deformation Across the Wasatch Fault
High resolution seismic and gravity data were acquired at a trench site across a Quaternary exposure of the Wasatch fault, Utah. Primary objectives of the high-resolution, CMP seismic study included: 1) testing the ability of reflection seismology to delineate unconsolidated stratigraphic units of Quaternary age in the upper 50 m of the study area; and 2) developing seismic processing techniques to suitably enhance the nonconventional, high-resolution data. Gravity data complemented the: seismic data and provided a constraint on the fault zone interpretation. These data revealed major fault locations in the unconsolidated sediment; however, gravity was of more assistance in mapping the location of the sediment-bedrock interface across the Wasatch Fault Zone. Specialized seismic acquisition equipment recorded signal up to 400 Hz. The 12-fold, high-resolution data were processed using methods similar to those of the oil industry. Static shifts (due in part to the over 35 m of topographic relief along the 154-m seismic profile) were a major interpretation problem that was resolved by refraction statics analysis. After processing, stratigraphic resolution was around 1 m, with Fresnel zone radii of 5 m on the deepest reflecting interfaces, at 40 m depth. Good resolution (80-300 Hz dominant bandwidth) in the stacked seismic data permitted a direct trench log-seismic profile comparison. The seismic data delineate fault locations and displaced. unconsolidated sediments as well as colluvial material abutting the main fault zone. The Wasatch fault is imaged as three diagonal traces offsetting gently dipping reflectors. Dip of the Wasatch fault is 70° W at the surface, and is estimated from the seismic data to be 45° W at 25 m depth. A cumulative displacement of 2 m across the antithetic fault system is observed in both the seismic data and the trench. Agreement between the trench log and the seismic data suggests the CMP reflection seismic method is a viable investigative tool in faulted, unconsolidated sediments.
Jack Pelton. "High-Resolution Seismic Imaging and Gravity Analysis of Deformation Across the Wasatch Fault" Abstracts of the U.S. Geological Survey, Central Region, Open-File Report OF 91-0582 (1991): 30.
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