Influence of Pre-Existing Strike-Slip Faults on Fault Development During a Subsequent Phase of Extension

The goal of this study is to investigate how high-angle strike-slip faults affect deformation patterns during a subsequent phase of extension. To accomplish this goal, I use scaled experimental (analog) models with wet clay and two phases of deformation, an initial strike-slip phase and subsequent extensional phase. In Series 1 models, the extension direction varies during the second phase. In Series 2 models, the degree of the strike-slip-fault development varies during the first phase. The first-phase, right-lateral strike-slip deformation consists of subvertical Riedel shears, right-lateral R-shears and left-lateral R’-shears that strike ~15 ° and ~85°, respectively, relative to the trend of the deformation zone. In Series 1 models, the maximum extension direction relative to the strike of the pre-existing R- and R’-shears controls the likelihood of reactivation, the sense of slip on the reactivated faults, and the orientation of new normal faults. Pre-existing faults that are closer to being subperpendicular to the extension direction are more likely to be reactivated as high-angle normal faults. Additionally, some of the pre-existing R-shears are reactivated as tension gashes. Pre-existing faults that are closer to! iii! being subparallel to the extension direction are more likely to be reactivated as oblique