Fault Interactions in an Experimental Model with Two Phases of Non-Coaxial Extension: Insights From Displacement Profiles

Abstract

This study used experimental (analog) modeling to investigate how fault geometries and interactions that developed during multiple phases of non-coaxial extension affected fault-displacement profiles. In the model, a homogeneous layer of wet clay underwent two phases of extension whose directions differed by 45°. We observed multiple types of interactions (such as nucleation, linkage, and offset) between first-phase faults and second-phase faults on the top surface of the model. These interactions influenced the displacement profiles for both first-phase faults (which commonly reactivated with oblique slip during the second phase of extension) and new second-phase normal faults. During the second phase of extension, many new normal faults nucleated at first-phase faults and propagated outward. These faults had a displacement maximum at the branch point with the first-phase faults, and their displacement decreased in the direction of fault propagation. Some new normal faults cut and offset first-phase faults as they propagated outward. The displacement profiles for these second-phase faults generally did not exhibit abrupt changes near the offset first-phase fault. The displacement profile for the offset first-phase fault, however, had an anomalously high value near the intersection of the two faults. Many second-phase faults linked with multiple first-phase faults, which produced composite faults with zig-zag geometries (with overall strikes oblique to both extension directions). For these zig-zag faults, displacement was higher along the first-phase fault segments that had linked with second-phase faults than along unlinked first-phase fault segments. In addition, the parts of the first-phase faults beyond the linked segment became inactive after linkage, creating abandoned fault segments at the ends of many first-phase faults. The fault interactions and displacement profiles in the clay model, specifically the modification of displacement on first-phase faults and variations in displacement along linked faults, are similar to those documented in basins that are inferred to have undergone multiple phases of extension (e.g., Norwegian North Sea and North Slope, Alaska).

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016