香港地区断裂构造的新活动性

NEW ACTIVITY OF THE FAULTS IN HONG KONG

香港地区主要分布有北东东-近东西、北东和北西向三组断裂。北东向断裂分布全区，燕山期有过强烈活动，第四纪早-中期仍有过活动，以后的活动性不明显。其余两组构造虽然具有不同的发展历史，但在新构造运动中为一组共轭构造。在晚更新世（距今9～11万年）仍有明显活动，全新世以来活动性相对较弱，全新世滑动速率为0．6～0.9mm／a。

There were three major fault systems which tend towards NE, ENE and NW respectively in Hong Kong area. Faults with activity within last 100, 000 years were considered to be the active faults.Among the three groups of faults,the NW and ENE trending faults were the main active faults, both of those often formed negative relief geomorphologically. Under the action of the prevailing tectonic stress field, the NW and ENE trending faults dislocated as a conjugate fault system, most of them showed signs of multi-stage activity with two stages of calcite vein and quartz vein intrusion.Thermoluminescence dating indicated an age of last motion in the order of 9000 ~ 11000 a. B. P,implying that activity continued to the early stage of Late Pleistocene. The activities of them in Holocene were rather weak, with dislocating rates of 0. 5~0. 9 mm/a. The NE trending faults were intensely active during Yanshanian Period, forming a series of Mesozoic-Cenozoic fault-trough basins along the NE fault zone. Fault activity diminished somewhat during the Quaternary Period. The frequency of microseismicity has increased somewhat since 1990, but there has been little change in magnitude. This is consistent with the overall picture in the large region since then, which also features an enhancement in the frequency of microseismicity. The seismic events were mainly distributed in the place where were also characterized by a relatively advanced stage of development of NW and ENE trending faults, thus reflecting a relationship between the two fault systems and local microseismicity.