THE QUATERNARY FAULT AND FOLD DATABASE OF ALASKA: GIS COVERAGES AND MAP COMPILATION TECHNIQUES

Alaska is the most seismically active region of the United States, however little information exists on the location, style of deformation, and slip rates of Quaternary faults. Historic earthquakes along the Denali fault (2002, M7.9), Aleutian subduction zone (1964, M9.2), and the Fairweather fault (1958, M7.9) attest to the importance of information related to Quaternary faults and their associated hazards. The Alaska Division of Geological & Geophysical Surveys (DGGS) has designed a Quaternary fault and fold database for Alaska in conformance with standards defined by the U.S. Geological Survey for the national Quaternary fault and fold database. The objective of the database is to produce an accurate, user-friendly and cohesive resource that provides summarized information on Quaternary faults, digital GIS files, and references for geologists, industry, and the public. The current GIS project includes thirty active faults which pose the greatest seismic hazard to Alaskans. Additional faults will be incorporated into the database as more information is developed. Here we present the GIS data for the state of Alaska and discuss some of the problems that were encountered and resolved during its compilation.

The Neotectonic Map of Alaska (Plafker et al., 1994) served as the starting point in the identification of Quaternary active structures. The mapped trace of each fault in the database was selected based on review of previously compiled literature (Craw et al., 2001). The majority of the faults included have been georegistered from 1:250,000-scale paper maps contained in 1970’s vintage and earlier bedrock maps, however each fault is evaluated on a case-by-case basis, with paper map scales ranging from 1: 20,000 to 1: 500,000. GIS fault attributes are consistent with the national guidelines and include relevant information such as fault name, age, slip rate, slip sense, dip direction, fault line type (well constrained, moderately constrained, or inferred), and mapped scale. Each fault is assigned a three-integer CODE, based upon age, slip rate, and how well the fault is located. This CODE dictates the line-type for the GIS files. Due to the limited level of knowledge on Quaternary faults, Alaska-specific modifications to the attributes have been made pertaining to slip rate and mapped scale.