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Harbin, China

The China Earthquake Administration , is mandated by the Law of the People's Republic of China on Protecting Against and Mitigating Earthquake Disasters of PRC to enforce the earthquake administration in the nation under the administration of State Council of the People's Republic of China.Some English text use the name Chinese Seismic Bureau . In older text, it was also referred to by its former name, National Earthquake Bureau or National Seismic Bureau . Wikipedia.

Jiang H.,China Earthquake Administration | Ding Z.,CAS Institute of Geology and Geophysics
Bulletin of the Geological Society of America | Year: 2010

In order to explore the Neogene evolution of East Asian winter monsoon circulation, grain-size analysis was conducted on the Neogene Sikouzi section, Guyuan, Ningxia, China, a relatively monsoon-sensitive region. The results show that most of the particles are fine, the sand-bearing samples (median grain size [Md] >63 μm) are less than 6.4%, and that all the grain-size distribution curves of representative samples have a similar pattern to those of eolian dust sediments on the Chinese Loess Plateau. Rare earth element (REE) patterns of eight samples from the Sikouzi section are all characterized by light (L) REE enrichments, relatively flat heavy (H) REE patterns, and slight negative Eu anomalies, similar to those of loess and the average upper continental crust. These lines of evidence point to a windblown origin of the Sikouzi fine sediments. Based on previous studies, the 10-70 μμm fraction of the Sikouzi sediments is mainly transported by the East Asian winter monsoon, and an increase in content of the 10-70 μμm fraction reflects strengthening of the winter monsoon. In contrast, sand grains in samples of Md >63 μμm are probably brought into the study area by rivers and streams linked with precipitation enhancement. According to stratigraphic variations in content of various fractions of the Sikouzi grain-size record, the Neogene evolution of the East Asian monsoon circulation can be divided into three stages. During the period 20.1-12.0 Ma, the 10-70 μm fraction holds the lowest values, whereas sand content usually shows high percent-ages, denoting a weak winter monsoon and a strong summer monsoon. After 12.0 Ma, the 10-70 μμm fraction increased substantially and remained at high values, while sand content showed a marked decline, indicating that the winter monsoon strengthened dramatically and the summer monsoon declined significantly. From 4.3 to 0.07 Ma, the winter monsoon strengthened further, as evidenced by the gradual increase in content of the 10-70 μμm fraction. This inference agrees well with the timing of glaciation development in the Northern Hemisphere. During the early to middle Miocene, the high values of both Md and sand content are mainly distribute in five intervals, 19.8-18.8 Ma, 18.0-17.5 Ma, 16.7-15.6 Ma, 14.3-13.7 Ma, and 13.0-12.0 Ma, corresponding to five periods of intense precipitation. The interval from 16.7 to 15.6 Ma is well correlated with the middle Miocene climatic optimum determined by the well-known Miocene Shanwang biota from eastern China. As for the other four periods, it is speculated that episodic growth of the East Antarctic Ice Sheet possibly shifted atmospheric fronts such as the Intertropical Convergence Zone (ITCZ) and thus carried water vapor further northward, leading to increases in regional precipitation on the northern midlatitude continent, including North China. © 2010 Geological Society of America. Source

Togo T.,Japan National Research Institute for Earth Science and Disaster Prevention | Shimamoto T.,China Earthquake Administration
Journal of Structural Geology | Year: 2012

Brunauer-Emmett-Teller (BET) surface area of quartz gouge was measured before and after shearing deformation at subseismic to seismic slip rates to determine how much of frictional work and fracture energy was consumed during grain crushing. Measurement of BET surface area provides more direct data on surface-area change than grain-size measurement does. Twenty-four experiments on quartz gouge composed of Ottawa sands or crushed quartz were conducted dry (with room humidity) or wet (with added water) at slip rates of 0.006∼1.3 m/s and normal stresses of 0.76∼3.37 MPa, using a high-velocity friction apparatus and a low to high-velocity friction apparatus. About 1 mm-thick gouge was placed between cylindrical specimens of Belfast dolerite of 25 mm in diameter. Results show that grain crushing absorbed only 0.02∼0.22% of frictional work and only 0.05∼1.06% of fracture energy under dry and wet conditions. Thus, grain comminution is unlikely to be an important energy sink at least for mature faults with well-developed slip zone. Surface area of gouge decreases with deformation at seismic slip rates. This and SEM observations suggest partial sintering due to frictional heating. Thus a simple scenario of grain crushing as an energy sink does not hold for estimating the energy budget during earthquakes. © 2012 Elsevier Ltd. Source

Lei J.,China Earthquake Administration
Journal of Geophysical Research: Solid Earth | Year: 2011

Detailed 3-D tomographic images of P and S wave velocity (Vp, Vs) and Poisson's ratio (σ) under the central and western Tien Shan orogenic belt are determined by using a large number of high-quality P and S wave arrival times from local earthquakes. The results show that under the Tien Shan orogenic belt high-Vp, high-Vs, and low-σ anomalies are revealed in the upper and middle crust, possibly indicating the existence of the Paleozoic crystalline basement rocks, while low-Vp, low-Vs, and high-σ anomalies appear in the lower crust and upper mantle, perhaps suggesting that the hot and wet material is upwelling under the Tien Shan orogenic belt from the mantle. Some high-Vp, high-Vs, and low-σ anomalies are tilted toward the Tien Shan along with the seismicity. These are found in the collision zones between the Tien Shan and the Tarim basin in the south and the Kazakh shield in the north and suggest the underthrusting of the Tarim and Kazakh lithosphere beneath the Tien Shan. Meanwhile, some low-Vp, low-Vs, and high-σ anomalies are imaged in other parts of these collision zones, perhaps indicating the intrusion of the hot and wet material into the crust from the upper mantle. These results indicate that both the upwelling of the hot and wet material and the underthrusting of the Tarim and Kazakh lithosphere may have played an important role in the mountain building. Under the Tarim and Fergana basins, low-Vp, low-Vs, and high-σ anomalies are revealed in the upper crust, while high-Vp, high-Vs, and low-σ anomalies are visible in the lower crust and upper mantle. These may reflect the existence of less compacted sedimentary material in the shallow crust and more highly compacted craton-like structures in the deeper crust and upper mantle under the basins. The Talas-Fergana fault shows an obvious tectonic boundary between central and western Tien Shan. The central Tien Shan displays high-Vp, high-Vs, and low- anomalies in the upper and middle crust, while western Tien Shan exhibits low-Vp, low-Vs, and high-σ anomalies. However, the pattern of seismic structure between central and western Tien Shan reverses in the lower crust. Such a correlation may extend down to the upper mantle, suggesting that the Talas-Fergana fault may be a lithospheric-scale boundary. Additionally, a columnar low-Vp and low-Vs anomaly is clearly observed around the turning point of the Talas-Fergana fault from the NWN to NWW trending orientations and may indicate that the fault provides a channel for the hot and wet material upwelling from the mantle to the surface. Copyright 2011 by the American Geophysical Union. Source

Lei J.,China Earthquake Administration
Journal of Geophysical Research: Solid Earth | Year: 2012

A high-resolution tomographic model of the upper mantle beneath the North China Craton (NCC) is determined using a large number of precisely hand-picked teleseismic P wave arrival times. The results are generally consistent with previous results but high-quality arrivals provide new insights into the dynamics beneath the NCC. Obviously north-south trending low-velocity (low-V) zones are revealed down to ∼300-400 km depth under the Shanxi rift and Tanlu fault zone, while a north-south trending high-velocity (high-V) zone representing the remainder of detached lithosphere is visible down to ∼200 km depth under the western portion of eastern NCC. High-V anomalies representing the detached lithosphere are detected at 200-400 km depth under central and eastern NCC. Under the Ordos block high-V anomalies are visible above ∼400 km depth, indicating intact lithosphere. Broad high-V anomalies representing the stagnant Pacific slab are imaged with a low-V anomaly from Datong volcano to the edge of Bohai Sea in the mantle transition zone beneath eastern and central NCC, suggesting that the Pacific slab has subducted to central NCC but with a gap. A continuously Y-shaped low-V structure is clearly imaged under Datong volcano and Bohai Sea from the lower mantle through this gap in the mantle transition zone to the upper mantle, indicating the existence of a lower mantle plume. These results suggest that in addition to the subduction of the Pacific plate, the plume has also played an important role in lithospheric destruction by thermal erosion of the asthenosphere and detachment of the lithosphere beneath the NCC. © 2012 American Geophysical Union. All Rights Reserved. Source

One of remarkable geological and geomorphological features in continental China is the presence of a north-south trending tectonic zone which separates the seismically active Tibetan Plateau to the west from the tectonically stable South China and Ordos blocks to the east. The zone also owns a name of "north-south seismic belt" as a large number of great historical earthquakes occur on it. The most recent one, the 2008 Wenchuan earthquake, attests its recent tectonic activity. In this review I take the Western Sichuan region as an example to probe the structural styles and kinematic pattern as well as deep geological process associated with tectonic deformation of the north-south trending zone. Through integrated studies on active faults, GPS crustal deformation, and geophysical structure, we show that deformation in the Western Sichuan is governed by interactions among three crustal blocks (Songpan, Chuandian, and South China) of distinctive rheological properties under the tectonic framework that eastward growth of the "soft" Eastern Tibet is blocked by the "hard" lithosphere of the South China block. The left-lateral Xianshuihe Fault continues to the north-south trending fault system without crustal shortening to form a bounding fault to limit the northern extend of the magnificent clockwise rotation of crustal material around the Eastern Himalaya Syntax. Upper crust of the three blocks is dominated by brittle deformation, whereas the ductile flow of lower crust would drag the brittle upper crustal blocks to move with respect to each other. The relative motions among the brittle upper crustal blocks cause strain accumulations among their bounding faults to generate large earthquakes. Deformation of the Western Sichuan region can thus be described in terms of combined model of rigid block movement and continuous deformation. We suggest this combined model can be applied to entire continental China. © 2012 . Source

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