By: W. R. Lund, editor
Geologic exposures in the Salt Lake City region record a long history of sedimentation and tectonic activity extending back to the Precambrian Era. Today, the city lies above a deep, sediment-filled basin flanked by two uplifted range blocks, the Wasatch Range and the Oquirrh Mountains. The Wasatch Range is the easternmost expression of major Basin and Range extension in north-central Utah and is bounded on the west by the Wasatch fault zone (WFZ), a major zone of active normal faulting. During the late Pleistocene Epoch, the Salt Lake City region was dominated by a succession of inter-basin lakes. Lake Bonneville was the last and probably the largest of these lakes. By 11,000 yr BP, Lake Bonneville had receded to approximately the size of the present Great Salt Lake.
Repeated normal-slip faulting has occurred at the ground surface in Utah during late Pleistocene and Holocene time. Most of this activity has been on the WFZ which traverses the Salt Lake City metropolitan area. The WVFZ has had at least six surface-faulting events in the past 13,000 years. Despite the close proximity to active faults, Salt Lake City has not yet been subjected to a large, destructive earthquake. Felt events have occurred, but only a few have caused appreciable damage.
Geologic units in the Salt Lake City metropolitan area generally provide adequate foundation conditions. The principal foundation problems are compressible, low-bearing-strength soils; collapse-prone soils; and liquefaction. Some shale units and the soils derived from them may be expansive. Numerous geologic hazards exist in the Salt Lake City metropolitan area. Movement on faults may cause ground rupture, ground shaking, tectonic displacement, ground failure including liquefaction, and seiches on the Great Salt Lake. Steep slopes create the potential for landslides, rock falls, debris flows, and snow avalanches. Streams and the Great Salt Lake experience flooding, and high ground-water conditions are common.
Pages: 66 p.
Location: Salt Lake County
Media Type: Paper Publication