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Global Positioning System (GPS) measurements in China indicate that crustal shortening accommodates most of India's penetration into Eurasia. Deformation within the Tibetan Plateau and its margins, the Himalaya, the Altyn Tagh, and the Qilian Shan, absorbs more than 90% of the relative motion between the Indian and Eurasian plates. Internal shortening of the Tibetan plateau itself accounts for more than one-third of the total convergence. However, the Tibetan plateau south of the Kunlun and Ganzi-Mani faults is moving eastward relative to both India and Eurasia. This movement is accommodated through rotation of material around the eastern Syntaxis. The North China and South China blocks, east of the Tibetan Plateau, move coherently east-southeastward at rates of 2 to 8 millimeters per year and 6 to 11 millimeters per year, respectively, with respect to the stable Eurasia.

Over 12 years of continuous monitoring of Changbaishan volcano in the border region of China and North Korea by means of volcanic seismicity, ground deformation, and volcanic gas geochemistry yields new evidence for magmatic unrest of the volcano between 2002 and 2006. In this so‐called “active period,” the frequency of volcanic earthquakes increased by about 2 orders of magnitude compared to that of the background “inactive periods.” The active period was also accompanied by ground inflation, high values of CO2, He, H2, and high ratios of N2/O2 and 3He/4He in volcanic gases released from three hot springs near the caldera rim. The monitoring evidence implies pressurization of the magma chamber, possibly caused by incremental magma recharge. The ground deformation data from both GPS and precise leveling are modeled to suggest the corresponding deformation source is at 2–60 km depth beneath the volcano's summit, where earthquake swarms were detected in 2002 and 2003. Our findings suggest that the magma chamber beneath Changbaishan volcano has awakened and resumed activity after remaining dormant since AD 1903. There is an urgent need to keep close watch on this active and very hazardous volcano in northeast China.

Based on the first arrival P and S data of 4 625 regional earthquakes recorded at 174 stations dispersed in the Yunnan and Sichuan Provinces, the 3-D velocity structure of crust and upper mantle in the region is determined, incorporating with previous deep geophysical data. In the upper crust, a positive anomaly velocity zone exists in the Sichuan basin, whereas a negative anomaly velocity zone exists in the western Sichuan plateau. The boundary between the positive and negative anomaly zones is the Longmenshan fault zone. The images of lower crust and upper mantle in the Longmenshan fault, Xianshuihe fault, Honghe fault and others show the characteristic of tectonic boundary, indicating that the faults likely penetrate the Moho discontinuity. The negative velocity anomalies at the depth of 50 km in the Tengchong volcanic area and.the Panxi tectonic zone appear to be associated with the temperature and composition variations in the upper mantle. The overall features of the crustal and the upper mantle structures in the Sichuan-Yunnan region are the lower average velocity in both crust and uppermost mantle, the large crustal thickness variations, and the existence of high conductivity layer in the crust or/and upper mantle, and higher geothermal value. All these features are closely related to the collision between the India and the Asia plates. The crustal velocity in the Sichuan-Yunnan rhombic block generally shows normal value or positive anomaly, while the negative anomaly exists in the area along the large strike-slip faults as the block boundary. It is conducive to the crustal block side-pressing out along the faults. In the major seismic zones, the seismicity is relative to the negative anomaly velocity. Most strong earthquakes occurred in the upper-mid crust with positive anomaly or normal velocity, where the negative anomaly zone generally exists below.

3‐D P‐wave velocity structure in crust and uppermost mantle in and around Wenchuan earthquake source region was studied using long‐term accumulated seismic travel time data in Sichuan–Yunnan region and aftershock data of Wenchuan earthquake. The result shows that shallow P‐wave velocity structure has good correlation with surface geology. Longmenshan fault zone is imaged as high P‐wave velocity region in 0~20 km depth. Pengguan complex and Baoxing complex are imaged as two local high velocity anomaly bodies. The upper to middle crustal high velocity anomaly bodies in Longmenshan fault zone control the distribution of aftershocks. At the southern part of the aftershock zone, aftershocks occurred only in the northeast of the high velocity body related with Baoxing complex; In the middle part, the distribution of aftershocks seems to be controlled by the high velocity anomaly body corresponding to Pengguan complex to some extent; In the northeast part, the high velocity body around Ningqiang–Mianxian may prevent the further extension of aftershocks to the northeast. The existence of upper crustal high P‐wave velocity zone in Longmenshan fault zone implies that the upper crust has relatively high strength, which may play an important role in obstructing the extrusion of Tibet Plateau material to east, and is prone to accumulate energy in deep depth. Yangzi Block is characterized by obvious high velocity region below 30 km depth, and its front edge extends to Tibetan Plateau with depth increasing and reaches to the west side of Longmenshan fault zone in the lower crust and upper mantle.

The S wave velocity structure within the depth of 0-100 km beneath digital seismic stations of Yunnan Province was obtained from teleseismic receiver function modeling. The results show that the crustal thickness changes greatly in Yunnan, reaching about 62 km in Zhongdian and Lijiang, and decreasing to 32-34 km in Jinghong, Simao and Changyuan in south. The thick crust extends from northwest to southeast, decreases in thickness and range, and is about 42 km thick around Tonghai. Its shape and range consist with Chuandian diamond block bounded by Xiaojiang and Yuanjiang faults. In the eastern and southern region, the crust is relatively thin, and the velocity contrast across Moho is obvious. In the areas with great variation of crustal thickness or thick crust area, the Moho is characterized by transition zone with high velocity gradient. In Yunnan region, S wave velocity structures show strong horizontal heterogeneity. Above the depth of 10 km, the S wave velocity in north area is obviously lower than that in south area, while within the depth of 10-20 km, the S wave velocity in north is higher than that in south. The velocity interface within crust is discontinuous, and the depth and range of lower velocity zones change with different seismic stations. There is no obvious crustal low velocity zone beneath nearly half of the stations. Influenced by the upper mantle in south area, within the depth of 40-50 km, S wave velocity in south area is higher than that in north, high velocity area extends to north, and the shape of low velocity zone tends to consist with Chuandian diamond block. The upper mantle velocity distribution within the depth of 70-80 km seems to be correlated to the distribution of strong earthquakes.

This study presents the results of the Rayleigh wave group velocity tomography in North\ud China performed using ambient seismic noise observed at 190 broadband and 10 very broadband\ud stations of the North China Seismic Array. All available vertical component time-series\ud for the 14 months between 2007 January and 2008 February are cross-correlated to obtain\ud empirical Rayleigh wave Green’s functions that are subsequently processed, with the multiple\ud filter method, to isolate the group velocity dispersion curves of the fundamental mode of the\ud Rayleigh wave. Tomographic maps, with a grid spacing of 0.25◦ × 0.25◦, are computed at\ud periods of 4.5, 12, 20 and 28 s. The maps at short periods reveal lateral heterogeneity in the\ud crust of North China, in good agreement with known geological and tectonic features. The\ud North China Basin is imaged as a broad low velocity area, while the Taihangshan and Yanshan\ud uplifts and Ordos block are imaged as high velocity zones, and the Quaternary intermountain\ud basins show up as small low-velocity anomalies. A well-defined low velocity zone in the\ud Beijing–Tianjin–Tangshan region is observed at 28 s period. The low velocity zone may be\ud associated with the upwelling of hot mantle material. The group velocity maps at 4.5, 12 and\ud 20 s are consistent with Bouguer gravity anomalies measured in the area of the Taihangshan\ud fault, that cuts through the lower crust at least

The Benzilan-Tangke deep seismic sounding profile in the western Sichuan region passes through the Songpan-Garze orogemc belt with trend of NNE. Based on the travel times and the related amplitudes of phases in the record sections, the 2-D P-wave crustal structure was ascertained in this paper. The velocity structure has quite strong lateral variation along the profile. The crust is divided into 5 layers, where the first, second and third layer belong to the upper crust, the forth and fifth layer belong to the lower crust. The low velocity anomaly zone generally exists in the central part of the upper crust on the profile, and it integrates into the overlying low velocity basement in the area to the north of Ma'erkang. The crustal structure in the section can be divided into 4 parts: in the south of Garze-Litang fault, between Garze-Litang fault and Xianshuihe fault, between Xianshuihe fault and Longriba fault and in the north of Longriba fault, which are basically coincided with the regional tectonics division. The crustal thickness decreases from southwest to northeast along the profile, that is, from 62 km in the region of the Jinshajiang River to 52 km in the region of the Yellow River. The Moho discontinuity does not obviously change across the Xianshuihe fault based on the PmP phase analysis. The crustal average velocity along the profile is lower, about 6.30 km/s. The Benzilan-Tangke profile reveals that the crust in the study area is orogenic. The Xianshuihe fault belt is located in the central part of the profile, and the velocity is positive anomaly on the upper crust, and negative anomaly on the lower crust and upper mantle. It is considered as a deep tectonic setting in favor of strong earthquake's accumulation and occurrence. Key words: Tibetan plateau; Songpan-Garze orogenic belt; deep seismic sounding; crustal and upper mantle structure; low velocity layer CLC number: P313.2 Document code: A *