UGS Compiles GIS Database Showing Geologic-Hazard Special-Study Areas for the Wasatch Front

From 1988 to 1995, the Utah Geological Survey (UGS) and Wasatch Front County Hazards Geologists completed geologic hazard special-study-area maps for the urban parts of Davis, Salt Lake, Tooele, Utah, Wasatch, and Weber Counties. These maps presently exist in a variety of formats ranging from modern Geographic Information System (GIS) digital databases to hardcopy mylar overlays. Recent work by the UGS addresses a long-term need to compile these maps into a uniform GIS database to enhance their utility to their wide range of potential users.

The 1:24,000-scale hazard maps show areas where surface-faultrupture, landslide, and debrisflow/ alluvial-fan-flooding special studies are recommended prior to development. These maps were originally compiled as mylar overlays. Similarly, Utah State University and the consulting firm Dames and Moore completed a series of liquefaction-potential maps in 1982–90 for much of northern Utah at a scale of 1:48,000 as hard-copy mylar maps. Local governments typically use these maps in geologic-hazard ordinances for land-use planning and regulation, and state and local government agencies also use them in developing predisaster mitigation plans and critical lands maps. The maps can also be used by homeowners, homebuyers, real-estate agents, and others to assess potential risks at particular sites of interest.

Working from the geologic-hazard and liquefaction-potential maps, we compiled four separate GIS datasets corresponding to surface- fault- rupture, liquefaction, landslide, and debris-flow/alluvial-fanflooding hazards. These four hazards have relatively uniform map data throughout the area covered by the GIS database. Data for other hazards (e.g., rock fall, stream flooding, problem soils) exist in some but not all areas. Because of the spotty data coverage, we did not compile GIS datasets for these other hazards.

The new GIS database will be the starting point for implementation of the Governor’s Geologic Hazards Working Group’s recommendation to update and improve existing Wasatch Front geologic-hazard maps (see article in the September 2007 issue of Survey Notes, and UGS Circular 104). Many new geologic maps and geologic-hazard reports have been completed since the original special-study-area maps were compiled, so the GIS database will facilitate formal updates. For ready access, the GIS database will be made available on compact disk from the UGS and posted on the UGS and Utah Automated Geographic Reference Center websites.