The NNE-trending Yangsan Fault, one of the major strike-slip faults, is located in the SE part of the Korean peninsula. A geometric bend of the fault trace is observed in the southern part of the fault. In this area, topographic differences based on aerial photo analysis are also observed between the western and eastern blocks. Furthermore, the local development of the Tertiary sedimentary rocks around the fault is recognized. The reasons for the development of those structural features and their relationships are studied in this work.
According to the geomorphic analysis and detailed field analysis, the Tertiary sedimentary rocks are distributed only in the western part of the fault and they contact with Cretaceous sedimentary rocks to the east along a thrust fault sub-paralleled to the Yangsan Fault. The detailed analysis of the Tertiary deposits indicates that the sediments are originated from the western mountains (granites) of the fault and are affected by compression after deposition. Although NNE-trending minor faults (sub-paralleled to the Yangsan Fault) generally show right-lateral sense, the NNW-trending folds associated with NNE-trending thrust faults indicate compression or transpressional reactivation along the pre-existing strike-slip fault.
Based on these structural patterns, a deformational evolution history is suggested here. A small Tertiary pull-apart basin was developed during the right-lateral movement due to the bend of the strike-slip fault. In a later stage, local reverse faults and folds were developed by E-W compression or reverse reactivation along the pre-existing strike-slip fault during the later left-lateral movement. This reactivation history is also recognized in granites around the fault.