Kattenhorn, S.A (1999)
Controls on Normal Fault Slip Behavior and Related Jointing
Normal fault evolution is dependent on many factors, including the stress state, stratigraphic layering, and mechanical interaction between fault segments. The nature of deformation around a fault, such as jointing in regions of increased stresses, is accordingly affected. An evaluation of these dependencies has application to the characterization of normal faults and associated joints in oilfields in extensional tectonic environments.
Normal faults slip when shear stresses resolved onto the fault surfaces exceed the frictional resistance to slip. Lithostatic stresses are compressive and keep fault surfaces in contact. Resistance to slip increases with depth in response to the increasing lithostatic load. In extensional environments, tectonic tension competes with the lithostatic compression and induces faults to slip in a manner dependent on the resultant total state of stress.
In 3D numerical models, when a constant remote tension is applied perpendicular to fault strike, the greatest slip occurs near the upper fault tip. Different slip behaviors are produced when the tectonic stress either increases or decreases with depth, and are thus dependent on the tectonic setting. The slip behavior, in turn, affects the tipline propagation tendency and thus the evolution of fault shape. 3D seismic data analyses indicate that sedimentary layering may also affect normal fault shape, resulting in wide faults. Joint orientations vary along the fault tipline and depend greatly on the characteristics of the total stress field. Such variations in joint orientations are observed in field examples of joints that formed in response to normal faulting in SE Utah.