Shallow-Depth Acoustic Reflection Profiling Studies on the Active Penglai-Weihai Fault Zone Offshore of the Northern Shandong Peninsula

Shallow- depth acoustic reflection profiling survey has been conducted offshore of the northern Shandong peninsula, and the late Quaternary offset features of the Penglai-Weihai fault zone are documented from more than ten shallow profiles. The fault zone passes through the offshore area between the Changdao islands and the Dazhudao island, and consists of a group of NW trending faults, which are dominated by normal and reverse slips with strike-slip component. The Penglai-Weihai fault zone is characterized by the obvious Quaternary activity, which can be divided by the Taocun-Dongdoushan fault in the North Huanghai (Yellow Sea) into two segments, the Changdao-Yantai segment and the Yantai-Weihai segment from west to east, respectively. The western Changdao-Yantai segment is a late Pleistocene active segment, where the uppermost fault points discovered in the survey are buried at more than ~30m bellow the sea bottom, and offset the early to middle late Pleistocene sedimentary layers, and no Holocene offset has been found. The eastern Yantai-Weihai segment is a mid Pleistocene segment on which no late Pleistocene offset has been found. The Penglai-Weihai fault zone is closely related to the occurrence of history strong earthquakes and modern small earthquakes, among them the 1548 Bohai strait Ms7 earthquake occurred on its western segment and the 1948 Weihai Ms6 earthquake on its east segment. The intersection regions of the Penglai-Weihai fault zone with NE striking fault zones are considered to be the likely places for the future medium to strong earthquakes.