Wasatch Fault (Utah), Detected and Displacement Characterized by Ground Penetrating Radar

Abstract

Digital ground penetrating radar (GPR) was used to detect and measure the displacement of the Wasatch fault zone at Brigham City, Utah. Optimum radar results were obtained from clean, fluvial-deltaic sand and gravel (quartz-rich) of the late Pleistocene, Lake Bonneville, Box Elder Creek delta (Provo level), which straddles the fault. From the north side of the Box Elder Creek delta, results clearly show three vertically-stacked radar facies of subsurface lithofacies; the middle and lower facies are displaced 7 to 8 m in post-Provo (14,000 years) and pre-Provo-aged sediments of Lake Bonneville. The upper radar facies of continuous broad concave reflections represent post-fault, slope-wash sediment eroded from the upthrown block which infilled the graben on the downthrown side. Two micro faults are also present. Less promising GPR surveys were conducted in and along several stream beds of the Weber River at Ogden, Little Cottonwood Creek at Sandy, American Fork River near Lehi, and Spanish Fork River near Spanish Fork. The main problem in the Wasatch fault zone was the large amount of human disturbance (highways, dams, hydroelectric turbines, high voltage powerlines, pipelines, irrigation headworks, buildings and access problems) near the mouths of mountain canyons where streams cross the fault. Many of these features cause severe noise problems especially with unshielded antennae.