Maerten: Slip Vectors on Intersecting Normal Faults

Numerical models based on linear elasticity theory predict asymmetric slip distribution with a steep slip gradient near the line of intersection of intersecting normal faults. They also predict a discrepancy between the direction of slip on the fault plane and the direction of resolved shear stress. Both variations in slip magnitude and direction are due to mechanical interaction between the faults with intersecting patterns. These interactions cause local perturbations of the shear stress field acting on the plane of the adjacent fault. Field observations from the Chimney Rock area of central Utah show that slickensides on normal faults cutting the Navajo Sandstone change rake away from the expected downdip direction as the intersection line with adjacent faults is approached. The sense and magnitude of this change in orientation are similar to those computed by using the numerical models. The good correspondence between field observations and theoretical results from this paper, not only provides insight into the mechanics of intersecting faults, but suggests that care is required when using standard inverse methods to compute paleostresses from slickenside data. The slickenside orientation near intersection lines will generally not be in the direction of the remote maximum shear stress as resolved on the fault plane. A parameter study of this change in orientation provides helpful results for evaluating field data prior to a paleostress analysis.