QUATERNARY TECTONICS OF THE BASIN AND RANGE PROVINCE OF NEVADA AND UTAH—FAULTS, FOLDS, AND GPS

The USGS has funded a 10-year effort to compile information on Quaternary faults and folds that are potential seismic sources for large surface-rupturing earthquakes throughout the U.S. The compilation consists of GIS-based maps of Quaternary faults and folds and a robust (i.e., >7,500 p.) database that will be accessible via the www. With the addition of the Basin and Range (B&R) data, the project is nearing completion and should prove to be quite useful for future seismic-hazard assessments and geologic comparisons to contemporary geodetic strain rates (i.e., Earthscope/PBO).

For this poster presentation, we focus on the B&R province. The map shows the above mentioned faults and folds, as well as GPS stations and paleoseismic study sites. Current campaign and continuous GPS stations are well positioned across the northern B&R, but existing paleoseismic studies have been conducted mainly along the Wasatch fault zone, central Nevada Seismic Belt, and Yucca Mountain area.

The map shows Quaternary fault and folds, their time of most recent movement, slip-rate category, sense of movement, and numeric identifier. The GIS data are maintained in ArcInfo and coupled to a File Maker Pro database that contains lengthy text-based descriptions, several of which will be displayed along with the map. The map itself shows >1,000 faults, the majority of which lie within the highly extended terrain of the B&R province in Nevada and western Utah.

For visual depiction of seismic hazards, we categorized Quaternary faults as <1.6 Ma, (black), <750 ka (blue), <130 ka (green), <15 ka (orange), and historic (>200 yrs, red) based on time of most recent surface rupturing. The 130 kyr time frame is probably most relevant for seismic-hazards assessments since it encompass several to many earthquake cycles on a typical B&R fault. The slip-rate categories (in mm/yr) are exclusive bins that separate relatively inactive faults (<0.2, thin lines) from active normal faults (0.2-1, medium lines) and moderately (0.2-1) to quite active (>1 to >5, thick lines) oblique- and strike-slip faults. Only the most active lateral-slip faults in the southwestern B&R move at rates >2 mm/yr.