Abstract: The present study deployed 20 micro-seismic stations in an area of ~1200 km² in west Urumqi, in the North Tianshan seismic zone and central-south boundary of the Jungar Basin, during May and October of 2010. The observations recorded by the seismic stations show that thestudy region is seismically active, but micro-earthquakes are scattered and do not concentrate along any regional fault belt. This distribution suggests that the regional seismicity is simultaneously controlled by different-order tectonics, which is typical for a wide and smooth basin-mountain transition zone where the study region located. A 3-D P-wave velocity model was inverted by micro-seismic tomography, and statistic resolution lengths were inverted for the 3D model. The P-wave velocity model provides upper-crustal structure information beneath the study region. The Urumqi piedmont depression has larger sedimentary thickness than the Chaiwopu depression, while the Chaiwopu depression has similar sedimentary thickness to the Bogeda anticlinorium. An east-west striking fault separating the former two blocks develops very well and the fault dips to the south. This fault may be the main fault of the north Tianshan seismic zone. A north-south striking fault separating the latter two blocks does not develop well. Besides, a local uplift is found at the depth range of 5~10 km in the northern Chaiwopu depression, which may indicate a good prospect of oil and gas exploration.

Key words: Deep structures, Passive seismic exploration, West Urumqi, Tianshan seismic zone