--> --> Fault Interactions in an Experimental Model with Two Phases of Non-Coaxial Extension: Insights From Displacement Profiles
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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-Previous HitphaseNext Hit faults and second-Previous HitphaseNext Hit faults on the top surface of the model. These interactions influenced the displacement profiles for both first-Previous HitphaseNext Hit faults (which commonly reactivated with oblique slip during the second Previous HitphaseNext Hit of extension) and new second-Previous HitphaseNext Hit normal faults. During the second Previous HitphaseNext Hit of extension, many new normal faults nucleated at first-Previous HitphaseNext Hit faults and propagated outward. These faults had a displacement maximum at the branch point with the first-Previous HitphaseNext Hit faults, and their displacement decreased in the direction of fault propagation. Some new normal faults cut and offset first-Previous HitphaseNext Hit faults as they propagated outward. The displacement profiles for these second-Previous HitphaseNext Hit faults generally did not exhibit abrupt changes near the offset first-Previous HitphaseNext Hit fault. The displacement profile for the offset first-Previous HitphaseNext Hit fault, however, had an anomalously high value near the intersection of the two faults. Many second-Previous HitphaseNext Hit faults linked with multiple first-Previous HitphaseNext Hit 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-Previous HitphaseNext Hit fault segments that had linked with second-Previous HitphaseNext Hit faults than along unlinked first-Previous HitphaseNext Hit fault segments. In addition, the parts of the first-Previous HitphaseNext Hit faults beyond the linked segment became inactive after linkage, creating abandoned fault segments at the ends of many first-Previous HitphaseNext Hit faults. The fault interactions and displacement profiles in the clay model, specifically the modification of displacement on first-Previous HitphaseTop 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).