A PRELIMINARY STUDY OF CRUSTAL DEFORMATION AND TECTONIC ACTIVITY IN XI'AN REGION
Wang Xin Zhao Zhecai (No. 2 Geodetic Brigade, State Seismological Bureau)
Based on large numbers of the data from repeated levellings and ground fissure investigations, by the help of geological data and dynamic informations of ground water, a synthetic analysis of the characteristic features of ground subsidence and ground fissures in Xi'an Eegion, as well as of their geneses, is made. The results are as follows:1. The ground subsidence in Xi'an region is generally in the form of a NE striking trough, with a secondary relief;2. Near the ground fissures the vertical deformation appears as a sudden-change zone, and about the same is the case in the vicinity of hidden fractures ;3. The ground fissures trend NE. Their characteristics indicate that they are of teetonogenetic type;4. The funnels caused by heavy groundwater pumping seem to have no evident bearing on the formation of the ground subsidence and fissures both in time and in space. Groundwater draft is not the main factor leading to the oceurences of the ground subsidence and fissures. We can preliminarily concluded that it is the result of the activity of the Qilianshan-Luliangshan tectonic system.