关键词: 活动断裂, 位移量, 位移速率, 珠江三角洲

Abstract: Fault structures are well developed in the Zhujiang Delta area. They can be classified into NW-, NE- and E-W-trending groups, most of which display distinct features of vertical differential movement. Since most of the faults are buried and their activities are relatively weak, the evidence of vertical dislocation are difficult to be identified directly in the field, and hence the amount of displacement along the faults can not be measured. Fortunately, a large number of drill holes have been drilled during the construction of the Zhujiang Delta, and a lot of data concerning the present altitudes above sea level of late Quaternary deposits and their ages have been measured and determined. Basing on the analysis of the formation and evolution of the Zhujiang Delta, we have selected a pair or some pairs of bore holes, which are close in position and may reveal the deposition time and environment of the same strata for comparative analysis. Then the vertical displacements along the faults can be determined according to the differences between the present altitudes above sea level of the same strata on both sides of the faults, and hence the dislocation rates can be calculated based upon the age data. We have calculated the late Quaternary vertical dislocation rates for 5 faults. The results show that the dislocation rates are within the range of 0.14～0.47mm/a. Among them, the vertical dislocation rate of the Xijiang Fault in the past 29,400 years is 0.44mm/a. The vertical dislocation rate of the Baini-Shawan Fault in the past 15,000 years is 0.39mm/a, while that in the past 11,400 years is 0.38mm/a. The vertical dislocation rate of the Gulao-Conghua Fault in the past 29,530 years is 0.47mm/a. The vertical dislocation rate of the Wuguishan north piedmont fault in the past 6,390 years is 0.19mm/a. The vertical dislocation rate of the Shougouling Fault in the past 29,800 years is 0.14mm/a, and that in the past 17,480 years is 0.19～0.21mm/a. All these results are of great importance to the project of detecting the active faults in major cities that will be carried out in the near future.

Key words: active fault, dislocation, dislocation rate, Zhujiang Delta