Kinematic and dynamic analysis of a low-angle strike-slip fault: The Lake Creek fault of south-central Idaho

A large, low-angle strike-slip fault with significant offset is present in south-central Idaho. The 40+ km long Lake Creek fault is oriented NXYW, 3O"SW and has a slip vector 18 km long, plunging 2" to N55"W. Slip was determined by restoring the offset of a map-scale fold trough. Thus, the fault is a dextral-normal fault with predominant dextral strike-slip and minimal normal dip-slip displacement. The present-day gentle dip of the fault appears to be the original dip since older folds and coeval to younger dykes in the area are not tilted. Several hypotheses for the origin of the low-angle fault are tested. Field and kinematic data support the interpretation that the fault formed as a low-angle strike-slip fault, not as a reactivated thrust fault nor in association with other regional fault systems. Based on fault array analysis and published experimental fault studies, the Lake Creek fault is interpreted to have formed as a low-angle strike-slip fault owing to a nearly axial compressive state of stress with a subhorizontal o,, and crustal anisotropy induced by NW-trending folds and SW-dipping axial planar cleavage. Copyright 0 1996 Elsevier Science Ltd