EVOLUTION AND ORIGIN OF THE GROUND FISSURES IN XIAN, CHINA

Large-scale extraction of ground water in Xian has resulted in signifi cant drawdown of the phreatic surface and in land subsidence across th is ancient capital of China. It has also triggered the rejuvenation of the normal faults in the upper portions of the Quaternary deposits un derlying the city, leading to surface rupturing and the development of ground fissure zones across the city. These ground fissure zones are structurally controlled in the sense that they are directly linked to the normal faults in the Quaternary deposits, all trending in an east- northeasterly direction. In essence, they are the surface expressions of the deeper faults under current drawdown conditions. The ground fis sures have resulted in extensive property damage along their paths of propagation. This paper describes their occurrence, their possible cau sative mechanism and the resultant damage. Of necessity, Xian will sti ll be dependent on ground water supply to a large extent in the years ahead. However, ground water extraction will have to be managed in an environmentally sustainable manner, in order to minimize the geologica l hazards associated with the ground fissures.