A high resolution deep seismic reflection profile of 68.9 km long across the Yinchuan faulted basin has been accomplished which for the first time yields the fine crustal structures, characteristics of deep fault system (Yellow River fault, Yinchuan fault and Eastern piedmont fault of Helanshan) of faulted basin in graben style, and the relationship between shallow and deep structures in Yinchuan basin. The results show that the upper crust is the region above a reflector with 8 s two‐way traveling time (about 20 km deep), there are many strata in the upper part of the upper crust where the continuity of different segment of stratum is good, and there is no obvious layered feature in the lower part of upper crust, where the geological structure is simple. The reflection energy is weak in the lower crust (8~13 s), where reflection events are not obvious. The crust‐mantle transitional zone (around 13 s) below the lower crust consists of a group of reflection sequences that have stronger energy and longer duration (1.5 s), and the thickness is about 4.5 km. Luhuatai fault and Yinchuan fault merge into the Eastern piedmont fault of Helanshan in the depth of 12~12.5 km and 18~19 km, respectively, the Eastern piedmont fault of Helanshan merges into Yellow River fault in the depth of 28~29 km, and Yellow River fault is a deep fault cutting the Moho. Yinchuan graben is a negative flower structure that is assembled mainly by Yellow River fault and secondarily by other faults. Based on the relationship between the Eastern piedmont fault of Helanshan and Yinchuan fault, it is thought that the Eastern piedmont fault of Helanshan played a controlling role in 1739 M=8 Pingluo‐Yinchuan earthquake.

It is known from the research of active tectonics that the northern margin of Tianshan mountains is characterized by typical intra‐continental active tectonics, and has multiple thrust faults and anticlines parallel to the mountains. In order to investigate the fine crustal structure and the geometry of major faults, as well as the deep‐shallow tectonic relations in the Ürümqi depression, a deep seismic reflection profile of 78 km long in near‐SN direction was completed in 2004. This profile is located in the transition zone between Tianshan Mountains and Junggar Basin to the west of Ürüumqi. The results show that the crust beneath the investigated area is divided into upper and lower crusts by a strong reflective zone at about 9~10.5 s TWT. The thicknesses of the upper and lower crusts are about 26~28 and 23~25 km, respectively. There are rich reflective layers and clear structural patterns above 5 s TWT as well as obviously different structural features along the profile. In the southern region of Xishan, the stacked deep seismic reflection section shows a series of EW‐striking thrust anticlines arranged in SN direction as well as a group of faults thrusting from south to north. All of these are influenced by a deep detachment zone. In the Xishan and Wangjiagou area, there is a set of steeply north‐dipping reflective layers and a group of faults slipping along the layers. The northern part of the profile shows the image of a typical sediment basin and its deepest depth is about 10~12 km. Between 6 and 9 s TWT, the stacked deep seismic reflection section shows disordered reflections with comparatively short continuation time and weak energy. These indicate that this part of the crust is evidently possessed of “reflection transparence”. The Moho transition zone occurs at 14~17 s TWT, and the zone thickness is about 9~10 km. In the studied area, the Moho discontinuity gradually deepens from north to south. Its depth is about 50~52 km at the northern segment of the profile and is about 54~55 km near north Tianshan. In the neighborhood of Xishan at the middle profile, the reflections from the boundary between upper and lower crusts as well as the Moho transition zone become misty while the shallow stratums show signs of uplift and fold, which may be related with the compression between Junggar basin and Tianshan mountains.

Based on P-wave, S-wave velocity structures and Poisson's ratio of the Maqin-Lanzhou-Jingbian seismic refraction/wide angle reflection profile, which crosses the northern Bayan Har block, the Qinling block, the Qilian block, the Haiyuan arcuate tectonic region, and the Ordos block, the crustal composition of the northeastern margin of the Tibetan plateau is studied and the geodynamic issues are discussed. At first, a set of feasible methods are systemically summed up, with which in situ P-wave velocities observed by deep seismic sounding can be corrected to the velocity under the special condition of temperature and pressure in the laboratory. It is the key to the methods to get temperatures in the crust using heat flow. The second, in situ P-wave velocities of the profile are corrected to the velocities under a standard pressure of 600 MPa and room temperature, the corrected velocities, combined with Poisson's ratio, are compared with laboratory measurements of ultrasonic velocities, and the crustal petrologic composition is determined in the study area. Results show that the average corrected velocity in the northeastern margin of the Tibetan plateau is 6.43 km/s, and the bulk crustal composition is felsic like the composition of the upper crust. In the Bayan Har block and southern part of the Qinling block, there is a lack of Vp > 6.9 km/s mafic rock layer in the lowest crust, instead there are alternating felsic and intermediate layers in the lower crust, and the bulk composition of the lower crust is felsic. In other blocks, there is a 2∼10 km thick mafic layer of Vp > 6.9 km/s and the bulk composition is intermediate in the lower crust. At last, on the basis of the crustal structure and composition in the northeastern margin of the Tibetan plateau, the opinion that crustal thickening occurred mainly in the lower crust is supported, and it is proposed that delamination possibly occurred in the lower crust of the Bayan Har block and southern Qinling block in the recent geologic time, which accelerated the uplift of the Tibetan plateau.

A comparatively complete layout chart is built by using small shot interval and receiver spacing in Tianjin-Beijing-Chicheng Deep Seismic Sounding profile. Based on the DSS data of the profile, the crustal structure and the tectonic coupling are studied in the rift-depression basin of eastern North China and Yanshan mountain uplift. Based on the existing researches in the region, the seismic structure environment is further analyzed in the eastern segment of Zhangjiakou-Bohai seismic belt. The result shows that the tectonic feature and interface structure of the crystalline basement in the rift-depression basin of eastern North China Craton are correlated with the geotectonic movement since Cenozoic era. The entirely different crustal structures between the stable Yanshan uplift with high velocity in the north and the incompact rift basin with low velocity in the south make the intergradational zone between the tectonic zoning line, Baodi-Tongbai and Ninghe-Changli faults, and Yanshan uplift provide a favorable structural environment for generation and occurrence of earthquakes in the eastern plain region of Zhangjiakou-Bohai seismic belt.

We parameterized the velocity model of North China using square nets. Grid spacing is 1.0km and there are 649×890×16 grid points in the whole velocity model. We obtained three‐dimensional (3‐D) upper crustal velocity structure of North China using 3‐D finite‐difference inversion method and Pg wave data from 30 deep seismic sounding (DSS) profiles in the studied area. The inversion results revealed that the low velocity rhombshaped North China basin is surrounded by high velocity uplifts, and North China basin is comprised of two large fault zones with an uplift in between. The two large fault zones are divided into several small basins. There are many shovel‐like normal faults in the studied area and the depth of crystalline basement varies significantly at different geological structures. All these results suggest that North China has very complicated geological structure and it has the deep structural background for strong earthquakes.