STRUCTURAL-ANALYSIS AND FAULT SEGMENT BOUNDARY IDENTIFICATION ALONG THE HURRICANE FAULT IN SOUTHWESTERN UTAH

Long normal fault zones are common in extending regions and can be div ided into segments with different geometries and faulting histories ba sed on surface observations. The boundaries between fault segments are important because they may be the sites of significant strain, may im pede rupture propagation, and may greatly influence the locations of e arthquakes. Because large geometric bends exist at some fault segment boundaries throughout the history of the boundary, we suggest that suc h bends can last throughout much of the life of the fault. We use faul t segmentation concepts to define a segment boundary and parts of two fault segments along the active Hurricane normal fault, southwestern U tah, U.S.A. We use Fault geometry, slip direction, shortening structur es in the hanging wall and footwall, and fault scarp morphology to ide ntify the fault segments and segment boundary. The fault strikes N13 d egrees W south of the boundary and N21 degrees E north of the boundary . Stratigraphic separation of geochemically identical Quaternary basal t in the footwall and the hanging wall suggests that the slip vector o f Quaternary displacement trends between N70 degrees W and S18 degrees W, and slickenlines, earthquake rakes, and dip analysis on syndeforma tional basalt further constrains the slip direction to N75-85 degrees W. Relative motion on the northern segment, termed here the Ash Creek segment, is purely dip-slip, and on the southern (Anderson Junction) s egment is dominantly dip-slip with a small dextral slip component. Fau lt scarps along the Ash Creek segment compared with offset gravels lac king scarps along the Anderson Junction segment suggest that the two s egments have different Late Quaternary faulting histories, which is in dicative of discrete fault segments. The Ash Creek segment is about 24 km long and the Anderson Junction segment is 19-45 km long, although the non-adjacent segment terminations remain poorly defined. The segme nt boundary zone consists of: (1) a small-scale hanging wall anticline that trends roughly normal to the fault; (2) a small-offset footwall thrust fault; and (3) space-filling imbricate normal faults in the han ging wall. Secondary structures suggest the segment boundary is a nonc onservative boundary. Copyright (C) 1996 Elsevier Science Ltd