LATERAL DISPLACEMENT VARIATION AND LATERAL TIP GEOMETRY OF NORMAL FAULTS IN THE CANYONLANDS NATIONAL-PARK, UTAH

The along-strike displacement variation of 20 well-exposed normal faul ts from the Canyonlands, Utah, is described and analysed. The displace ment profiles of these faults are highly variable, and most irregulari ties can be related to fault segmentation. Many of the profiles are hi ghly asymmetric, and this can be related to mechanical interaction in some cases. Linear displacement tapers are observed towards all the la teral tips, but the percentage of trace length over which this linear taper occurs is highly variable. Three distinct lateral tip geometries are recognised, referred to informally as types A, B and C. Type A ti ps have a simple Mode III displacement geometry, Type B tips are chara cterised by a zone of extensional 'fissures' surrounding the fault tip , and Type C tips are characterised by the development of a monocline beyond the tip. Lateral displacement variation towards tips was analys ed by measuring displacement gradients from systematic positions along the fault trace. Lateral displacement gradients measured for 39 tips exhibit a wide range of values (0.016-0.25). Fourteen of these lateral tips are regarded as 'active' since they exhibit signs of recent surf ace rupturing. These active tips have a similar range of lateral displ acement gradients (0.019-0.25) to the overall population. Lateral disp lacement gradients were correlated with fault parameters such as lengt h, length/maximum displacement (for faults and segments), and proximit y to adjacent faults. No positive correlations were found. We suggest that the large range of lateral displacement gradients is mainly due t o interactions between neighbouring faults. Additional complexities ar e likely to have resulted from strength heterogeneities related to joi nting, from local variations in remote loading stresses and the fricti onal properties of the fault surfaces, and from processes related to s egment linkage. (C) 1998 Elsevier Science Ltd.