关键词: 海域活断层探测, 千里岩断裂, 声波探测, 山东半岛

Abstract: It is the first time that several profiles of acoustic survey have been conducted across the Qianliyan Fault in the northern part of the South Yellow Sea. According to the difference of the late Quaternary fault activities revealed by the acoustic survey,the Qianliyan Fault may be divided by the Chaoliandao Fault into two segments. The southern segment is not active since the late Pleistocene,no offset in late Pleistocene strata has been observed on the acoustic profiles to the southeast of Rizhao. The northern segment is active in the late Pleistocene,normal faults are observed on the acoustic profiles west of Qianliyan island and offset the middle and upper part of the late Pleistocene layers,but no offset has been found in the latest Pleistocene and Holocene strata. In addition,it is found that the Qianliyan Fault offsets the late Pleistocene strata in the sea region 15km east of Shidao,Rongcheng County. In summary,the northern segment of the Qianliyan Fault is active in the latest Pleistocene in the sea region from the west of Qianliyan Island to the east of Shidao. Besides the Qianliyan Fault,other faults develop in the region to the southeast of the Qianliyan Island,which show obvious late Pleistocene active evidence. Therefore,the relative uplift status of the block where the Qianliyan Island lies on may be related to the late Pleistocene tectonic activities including that of the Qianliyan Fault. Both modern and history seismicity are relatively week in the region along the Qianliyan Fault. Since the establishment of the seismograph network in this region,no earthquake with magnitude equal or larger than 5and no small earthquake clusters have occurred along the Qianliyan Fault and in the surrounding area. The only historic earthquake is the 1932 M6(1/2) southern Yellow Sea earthquake which occurred in the sea region 28km southeast of the Qianliyan Fault. It is obviously that the seismicity is not concordant with the late Pleistocene active features of the Qianliyan Fault. Above all,the Qianliyan Fault is over 100km long from the Qianliyan Island to the offshore near Shidao and it is obviously active in the latest Pleistocene,the probability of the occurrence of a some M6.5 earthquake along the Qianliyan Fault should be considered in the practice of earthquake prediction and seismic hazard analysis.

Key words: offshore active fault survey, Qianliyan Fault, acoustic sounding, Shandong Peninsula