Fault activity on the inner continental shelf of the SE Korean Peninsula associated with back-arc opening and closing in the NW Pacific subduction zone

Abstract

The SE continental shelf of the Korean Peninsula was deformed by back-arc rifting associated with the separation of the SW Japan Arc in the Cenozoic. However, the deformation character of the inner continental shelf of the peninsula is not well known. High-resolution seismic profiles reveal a structure representative of a strike-slip duplex on the inner shelf that consists of bounding master faults joined by an array of splay faults. Structural interpretation of this duplex enables us to explain the deformation of the inner shelf with three tectonic stages: (1) generation of normal rift faults in the early stage of back-arc rifting in the late oligocene, (2) sinistral slip on the rift faults under northward compression induced by back-arc closing since the Middle Miocene, and (3) dextral slip on the rift faults induced by ENE–WSW compression since the early pliocene. In the first stage, back-arc rifting generated NNE–SSW oriented rift faults. In the second stage, the interior region between a pair of outer rift faults was subjected to NE–SW extension, creating a duplex with the generation of second-order splay faults oriented NW–SE. In the third stage, the interior region was deformed by ENE–WSW compression, causing convex upward stratigraphic reflectors in individual fault blocks. Our study suggests that the geologic deformation of the continental shelf of the SE Korean Peninsula, up to the inner part, is tied closely to the tectonic evolution in the back-arc region in the Pacific subduction zone. © 2023, The Author(s), under exclusive licence to Springer Nature B.V.