FAULT SEGMENTATION, LINKAGE, AND EARTHQUAKE HAZARDS ALONG THE SEVIER FAULT, SW UTAH

Fault segmentation and linkage theories are applied to different long (>70 km) faults around the world. The theories imply that faults initiate as separate faults, propagate, and ultimately link to form a long fault. Fault linkage models include situations in which separate faults originally overlap or underlap. In addition, separate faults may link along new breakthrough faults or by one fault capturing another. Fault capture occurs between overlapping faults where one fault propagates more quickly and links to a second fault near its center. Segment boundaries may occur at linkage zones and include geometric, structural, and earthquake types. The purpose of this study is to document and determine how two sections of the Sevier fault (SF) linked, what type of segment boundary formed, and assess the earthquake and slope failure hazards for the region.

The SF is a steeply dipping, down to the west, segmented long (~250 km) normal fault located in the High Plateaus subprovince of the Colorado Plateau. A 17 km section from Orderville to north of Glendale, UT was studied. Data analyses suggest the SF linked by fault capture and formed a geometric bend. At the geometric bend and 8 km north, two relay ramps were documented further suggesting linkage occurred in this zone.

Although no Holocene ruptures were documented along the SF, offset Quaternary basalt indicates Quaternary movement. Earthquakes located near the trace of the SF suggest it may be active. Landslides and rockfalls are common along the 73.2 m to 182.9 m high fault escarpment.

We suggest that the SF is a segmented, long normal fault that initiated as more than one isolated fault and then linked to form the fault we see today. Linkage in the study area occurred by fault capture with the formation of two relay ramps and a geometric bend. Because the SF may be active seismic risk is posed to the communities and roadways in the region.