Edited By: William R. Lund
This publication presents four investigations that provide new geologic and paleoseismic data on the Washington fault zone in southwestern Utah and northwestern Arizona. (1) New 1:24,000-scale geologic mapping shows the location and length of young surface ruptures and the relative ages of displaced surficial deposits along the fault zone. Based on the mapping, the former Northern section of the fault zone has been subdivided into the Fort Pearce and Washington Hollow sections. (2) A paleoseismic trenching investigation of a scarp on a latest Quaternary alluvial fan in Arizona that provides information on paleoearthquake timing, displacement, and recurrence for the Fort Pearce section, which traverses the St. George metropolitan area. (3) Trace element and major oxide geochemical correlation and radiometric dating of volcanic flows displaced across the fault that provide early to middle Quaternary vertical slip-rates for the Fort Pearce and Sullivan Draw sections of the fault.. (4) A geotechnical investigation that provides information on fault locations, paleoearthquakes, and displacement no the Fort Pearce section. These investigations show the Fort Pearce section of the Washington fault zone has experienced at least two surface-faulting earthquakes in the Holocene and a minimum of five earthquakes in the past ~68 ka.