Characteristics Timing And Hazard Potential Of Liquefaction Induced Landsliding In The Farmington Siding Landslide Complex Davis County Utah

The Farmington Siding landslide complex is in Davis County, Utah, about 25 kilometers north of Salt Lake City. The landslide complex covers approximately 19.5 square kilometers and is one of 13 late Pleistocene/Holocene features along the Wasatch Front mapped by previous investigators as possible liquefaction-induced lateral spreads. The Farmington Siding landslide complex is in a largely rural area, but state and interstate highways, railroads, petroleum and natural-gas pipelines, and other lifelines cross the complex. Continued population growth along the Wasatch Front increases the likelihood of urban development within and adjacent to the landslide complex. Development along the Wasatch Front has proceeded with little consideration of hazards associated with liquefaction-induced landslides. Slope-failure mechanisms, extent of internal deformation, and timing of landslide events are poorly understood, and these factors must be evaluated to enable local governments to effectively plan for development and implement hazard-reduction strategies as needed. The purpose of this study is to assess the hazard associated with future liquefaction-induced landsliding within and adjacent to the Farmington Siding landslide complex by evaluating slope-failure modes and extent of internal deformation within the complex, inferring the geologic and hydrologic conditions under which landsliding occurred, determining the timing of landsliding, and evaluating the relative likelihood of various earthquake source zones to trigger liquefaction-induced landsliding. We chose the Farmington Siding landslide complex for this study because of the distinctiveness of geomorphic features on the northern part of the complex and the presence of landslide deposits that are clearly of different ages. Furthermore, because much of the area is rural, appropriate land-use planning measures can still be implemented to protect future development.

The purpose of these guidelines for investigating geologic hazards and preparing engineering-geology reports, is to provide recommendations for appropriate, minimum investigative techniques, standards, and report content to ensure adequate geologic site characterization and geologic-hazard investigations to protect public safety and facilitate risk reduction. Such investigations provide important information on site geologic conditions that may affect or be affected by development, as well as the type and severity of geologic hazards at a site, and recommend solutions to mitigate the effects and the cost of the hazards, both at the time of construction and over the life of the development. The accompanying suggested approach to geologic-hazard ordinances and school-site investigation guidelines are intended as an aid for land-use planning and regulation by local Utah jurisdictions and school districts, respectively. Geologic hazards that are not accounted for in project planning and design often result in additional unforeseen construction and/or future maintenance costs, and possible injury or death.

The purpose of this study is to evaluate the potential for future movement of the landslides during earthquakes to determine the hazard these features may pose. Goals of the study were to: (1) determine when landslide movement occurred, (2) determine the failure mode (lateral spread versus flow failure), (3) determine if recurrent movement has occurred, (4) correlate, where possible, through radiocarbon dating, the timing of landslide movement(s) with the paleoseismic record from fault studies along the Wasatch Front, and (5) assess the current hazard from liquefaction-induced landslides along the Wasatch Front. Once the study was underway, it became evident that not all 13 landslides were liquefaction induced, or even landslides at all. Thus, an additional goal of the study became determining which of the 13 mapped landslides were liquefaction induced, which were not liquefaction induced, and which were formed by other processes. 40 pages + 16 plates