关键词: 合浦-北流断裂, 合浦盆地, 活动性

Abstract: Hepu-Beiliu Fault starts from Beibuwan sea area in the southwest,extends northeastwards continually though Hepu,Bobai. The total length of the fault exceeds 400 kilometers and the general strike of the fault is 40°～60°. The Hepu-Beiliu Fault comprises two branches-the east branch and the west branch. The west branch stretches from the southwest of the Hepu Basin lying in the lower reaches of the Nanliu River towards the northeast. This paper discusses the activity of the fault segment in the Hepu Basin in the west branch of Hepu-Beiliu Fault from the following three aspects. Firstly,in view of the geological topography,fault-scarps develop widely in the Hepu Basin segment of the west branch and the linear feature of the scarp distribution is notable; Secondly,some exact locations that the fault crosses are investigated by high-resolution seismic reflection profiling; Finally,in order to evaluate the activity and their times of the Hepu Basin segment of the Hepu-Beiliu Fault,borehole drilling is carried out to find out the dislocated stratum of the fault and take samples for laboratory dating to define the latest activity time of the fault. Based on the fault chronology results,the latest active era of this segment(the Hepu Basin segment of the Hepu-Beiliu Fault)is concluded in the late era of the lower Pleistocene. The fault slip displacement is about 10 meters. This fault is covered by the strata of the middle to upper of mid-Pleistocene,which means that the activity level of this segment became lower,or it has been inactive since the late eva of mid-Pleistocene.

Key words: Hepu-Beiliu Fault, Hepu Basin, activity