山东半岛北部近海海域北西向蓬莱—威海断裂带的声波探测

Shallow-depth sonic reflection profiling studies on the active Penglai-Weihai fault zone offshore of the northern Shandong peninsula

在山东半岛北部近海海域进行了多条剖面的声波探测,初步查明了蓬莱-威海断裂带的基本活动特征.该断裂带由一系列北西走向的次级断层组成,主体在长岛至大竹岛之间的海域,多数断层以正断兼有走滑运动为主,部分断层具有逆冲运动性质.断裂带在第四纪活动明显,以北东向桃村-东陡山断裂在海域的延伸段为界,蓬莱-威海断裂带可分为两段:长岛-烟台段和烟台-威海段.西段长岛-烟台段为晚更新世活动段,多数次级断层上断点埋深位于海底以下30m,明显错断了中更新世地层,部分断层明显错断了晚更新世早期地层,有些断层达到晚更新世地层中部,但没有发现全新世地层错动现象.东段烟台-威海段为中更新世活动段,没有发现晚更新世地层错断现象.蓬莱-威海断裂带对历史地震和现代小震活动具有明显控制作用,其中1548年7级地震发生于断裂带西段,1948年6级地震发生于断裂带东段.蓬莱-威海断裂带与北东向断裂交汇区是中强地震发生的有利部位.

Shallow-depth sonic reflection profiling survey has been conducted on the offshore of the north of the 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 between the Changdong 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 Yellow Sea into two segments, the Changdao-Yantai segment and the Yantai-Weihai segment from east to west, respectively. The western Changdao-Yantai segment is a late Pleistocene active segment, where the uppermost fault points discovered in the 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 modem 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.