Crustal structure in northern margin of Tianshan mountains and seismotectonics of the 1906 Manas earthquake

Introduction The Tianshan orogenic belt between the Tarim and Junggar basins has re-uplifted in Cenozoic due to the collision and the northwards push-compression of Asia-India plate. The special active tectonic zones have been formed along both south and north margins of the Tianshan mountains (FENG, et al, 1991). The Tianshan seismic belt is one of the major seismic belts in China. A se-ries of strong earthquakes occurred in two flanks of the Tianshan mountains in 20th century, such as …

Crustal structure in northern margin of Tianshan mountains and seismotectonics of the 1906 manas earthquake

The thin-skinned structure in the crust of the northern Tianshan piedmont is explored by an 86-km-long, NS-trending deep seismic reflection profile through the ürümqi depression of the north margin of the Tianshan mountains. On the CDP stacking section, the first- and second-row parallel to anticlines in the north margin of the Tianshan mountains are shown on the segment to the south of the Shihezi. The detachments, corresponding to the reflection events at TWT 2.5–3.0 s and 5.5–6.0 s respectively, join the crustal deep structure to the reverse fault-fold zone. The Manas thrust extends downwards in listric shape, merges into the detachment at about TWT 2.5 s and joins to the Qingshuihe thrust. The reflection events on 5.5–6.0 s are corresponding to the main detachment, which joins the lower Manas anticline, and finally converge to the Junggar Southern Marginal Fault. A 12–14 km-thick sedimentary basin exists on the region in the north to the Shihezi. The depth of the Moho discontinuity beneath the Junggar basin is about 45 km, and increases southwards to 50 km. The crustal structure inferred from the deep seismic sounding profile and the Bouguer anomaly in the same region is consistent with the image from the deep seismic reflection profile. The seismogenic model of the 1906 Manas earthquake is related to the fault system, which consists of the Qingshuihe thrust, the detachments and the shallow Manas ramp. Fondation item: State Natural Scientific Foundation of China (No. 49734240), the China Seismological Bureau in the Project 95-04-09 and the Xinjiang Uygur Autonomous Region in the National 305 Project 96-915-07-03. Contribution No. 00FE2009, Institute of Geophysics, China Seismological Bureau. The data collection in field is assisted by the Sichuan Mountainous Oil Seismics Company.