Geodetic deformation in northern Qilianshan margin and Hexi Corridor area, Northwest China and its relation to the earthquake

Northern Qilianshan margin-Hexi Corridor area is situated in the northern margin of Qinghai-Xizang Plteau. Because of the collision of the Indian plate and the Eurasian plate from late Mesozoic to early Cenozoic and their long-distance effect of the continuous compression up to now, northern Qilianshan margin-Hexi Corridor area is a strong present crustal movement zone, and geodetic deformation is one of the main forms of the movement. The geodetic deformation monitoring shows the largest vertical deformation rate is +15mm/a in upwelling area and -15mm/a in subsidence area. The relative changes of the upwelling and subsidence between the Qilianshan and Hexi Corridor are related to the earthquakes in the area. When the Hexi Corridor area is subsiding and Qilianshan area is upwelling, there are many earthquake activities, while the Hexi corridor area is upwelling and Qilianshan area is subsiding, there are few earthquake activities. That is a result from the tectonic setting of compression stress field. The GPS horizontal crustal displacement monitoring shows that the horizontal crustal displacement is toward the East and the displacement rate is rapid (the fastest rate is more than 10mm/a). And the horizontal deformation rate changes more in the southern part than in the northern part, more in the eastern part than in the western part. The changes of the horizontal deformation rate are related to the active faults and the different rate zone divided by the main active fault as boundary. Vector of the horizontal crustal displacement is identical to the glide direction along the seismic fracture shown by mechanism interpretation of the quake-source on 2002, Yumen earthquake.