A SERIAL NE FAULTING FOR PLIOCENE TO HOLOCENE, SE. KOREA

Since 12Ma ago, the southeastern block of Korean peninsula had rotated to clockwise because of opening the East Sea. A master fault of the block, YTL (Yonil tectonic line), strikes N20W and is ca. 60km long. The middle part of YTL is 5 km away toward the northeast from UFT (Ulsan fault) of N20W and is parallel to UFT. Both the northwestern and southeastern extensions of YTL join to UFT obliquely. In between those two faults, a lot of late Pleistocene fault of NNW-NS has occurred with short length of 1.5-0.5km. Those faults show left-overstepped pattern and have left lateral strike-slip fault movement sense. Those faults form a half of positive flower structure toward the southwestern side of the block, because there are well-developed topographic slopes and lowland on the southwest of YTL and UFT. The northeastern side of those two faults is composed of highland, where there is not any shear fault as a flower structure. Pleistocene faulting has been formed by confining EW stress from the east since Pliocene. Altitudes of northeastern marine terraces on the hanging wall of UFT are higher than that of the southwestern block. Within the trans-rotated block, a serial NE faulting had occurred as bookshelf and each fault-bounded block shows left lateral strike-slip movement sense due to trans-extension. The YTL and UFT did a role of master fault for paralleled NE faults. Horizontal distance among NE faults is about 7-5 km. The oldest NE fault, Ochun Fault, is about 35 km long and has a significant uplift on the southeastern block. The second fault, Joogjun Fault, to the southeast is shorter than that of the first and pulled up the southeast. The third, Eoil Fault, is ca. 20 km long and reversed the southeast. The final one named GHL (Gampo-Hyodongri tectonic line) is shorter than the third and shows uplift of the southeastern block. Altitudes of marine terraces of the coastal block, which is the hanging wall side of GHL, have been lift up relatively. It reveals that the scale and intensity of faulting get to reduce toward the southeastern coast and that age of faulting might become younger to the southeast. The serial NE faults had been transtensional shear fault and has changed to reverse sense to the west since Pliocene. The coastal block receives passive confining pressure from the closing East Sea.