Abstract:

Abstract:  The Hexi Corridor (37°17′N to 42°48′N; 93°23′E to 104°12′E) is located in the northeast margin of Tibetan Plateau active block region. The deep fault zones trending WNW (northern boundary fault of the Qilianshan) and NNE (Altyn fault zone) are well developed. Medium and strong earthquakes ever occurred in history in these regions, especially at the junction region of Qilianshan seismotectonic zone and northsouth seismotectonic zone. After Wenchuan  earthquake Ms 80 occurred at 14:28:01.42 CST on 12 May 2008, all regions except Xinjiang, Jilin and Heilongjiang in China were affected by the great quake. It is a remarkable problem that how strong the coming earthquake in the Hexi seismic belt may be in the future time. In this paper, the authors have measured strontium and helium isotopic compositions of groundwater in Zhangye, Wuwei and Jiuquan Basins. It is concluded that the groundwater in these three basins are not originated from the runoff of Heihe River, Shiyanghe River or Shulehe River respectively, but from the supply of rainfall in the Qilianshan mountain front, which feeds the deep fault zones and then flows up over the Earth surface. The groundwater in different areas have different cycling routes. Therefore, the fault zones within the Hexi Basin are strongly active at present. The Yumen, Gaotai, Minle, and Yongchang Counties are located at or nearby the junction areas of the deep fault zones, so the occurrence probability of medium and strong earthquake in the future is quite high within the regions. It should be stressed to enhance the realtime monitoring of groundwater in the regions.

Key words: Key words: strontium isotope; helium isotope; Hexi Corridor; groundwater; earthquake activity