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Zhu X.,Chinese Institute of Crustal Dynamics
Earthquake | Year: 2015

Earth resistivity observation is from the DC power supply to more powerful pulse power supply with sinusoidal AC power supply, but the earth capacitive effects will cause observation error. This paper analyzes the effects of earth capacitance from the supply perspective. According to the method of equivalent circuit electronics, I put forward the concept of the equivalent capacitance of the earth. The relationship between equivalent capacitance of the earth and frequency and polar distance has been found based on experiment observations. ©, 2015, Science Press. All right reserved. Source

Xu J.S.,Chinese Institute of Crustal Dynamics
Applied Mechanics and Materials | Year: 2014

Determining the in-situ stress of wall rock is important for the underground cavern project. The three-dimensional (3-D) stress measurement, which is obtained by hydraulic fracturing stress measurement via measuring the stresses in boreholes with three different orientations, has been applied for the designation of cavern project. However, there are few examples that can demonstrate the reliability of 3-D stress measurement method. In this study, we showed one example of the 3-D stress results measured by hydraulic fracturing in Western China. The measured results, especially the dip angles of the maximum principle stress are consistent with those determined by focal mechanism of nearby earthquakes. This consistence indicates the reliability of the 3-D stress results by hydraulic fracturing and an expected application for regional geostress study. © (2014) Trans Tech Publications, Switzerland. Source

Zhang Y.,China Railway No.5 Engineering Group Co. | Xing B.,Beijing University of Technology | Song C.,Chinese Institute of Crustal Dynamics
Modern Tunnelling Technology | Year: 2014

Affected by staged excavation, stress-strain nonlinear variation may occur inside the surrounding rock of a tunnel. In high-ground-stress areas, this mechanical effect tends to be even more obvious and can cause serious geological disasters like rockbursts and wall caving, etc. Taking the construction of the Meihuashan tunnel in Fujian as an example, this paper analyzes the interaction of the excavation steps and the change rule of the 3D stress field and strain field in the tunnel by establishing a 3D excavation numerical model with 3D -Sigma software, using the measured stress data as a boundary condition and determining the inputs of the rock mass with the Hoek -Brown strength criterion. The results show that: because of high ground stress, compressive stress concentration occurs at the tunnel crown and shear stress concentration occurs at the spandrel, which may cause brittle failure at the tunnel wall; previously excavated tunnel sections may be affected by subsequent excavation, making the stress concentration effect more obvious and the failure of the surrounding rock more serious; the actual rockburst locations correspond with the locations of maximum compressive stress concentration and maximum shear stress concentration in simulation analysis. The numerical simulation can clearly reveal the mechanism and the possible law of the rock burst, providing strong technical support for engineering applications. Source

Qiu Z.-H.,Chinese Institute of Crustal Dynamics | Chi S.-L.,Hebi Seismological Bureau
Earthquake | Year: 2013

While a traditional seismograph records the variations of displacement with time at a point, a tensor strainmeter monitors the variations of the spacial gradient of displacement. An YRY-4 borehole strainmeter at Guza, Sichuan province, recorded three local seismic events at the sampling rate of 100 sps for the first time. At this high sampling rate, the data of the YRY-4 demonstrated a satisfying degree of self-consistency and sufficiently high credibility. The observation shows that P wave strain contains areal strain components as well as shear strain component. It gives direct evidence for the property of P wave. According to the theory of seismology, P wave is clarified to have no rotation, but it has volumetric strain and shear strains. Source

Chen Y.,CAS Institute of Geology and Geophysics | Zhang Z.,CAS Institute of Geology and Geophysics | Sun C.,Chinese Institute of Crustal Dynamics | Badal J.,University of Zaragoza
Gondwana Research | Year: 2013

In addition to crustal thickening, distinctly different mechanisms have been suggested to accommodate the huge convergences caused by the continental collision between India and Eurasia. As the transition zone between the two grand tectonic domains of Asia, the Tethys and the Pacific, east Tibet and its surrounding regions are the ideal places to study continental deformation. Pervasive rock deformation may produce anisotropy on the scale of seismic wavelengths; thus, seismic anisotropy provides insight into the deformation of the crust and mantle beneath tectonically active domains. In this study, we calculated receiver function pairs of radial- and transverse-components at 98 stations located in Sichuan and Yunnan provinces, China. We selected 7423 pairs with high signal-to-noise ratio (SNR) and unambiguous Moho converted Ps phases (Pms) to measure the Pms splitting owing to the crustal anisotropy. Both the crustal thickness and the average crustal Vp/Vs ratio were calculated simultaneously by the H. k stacking method. The geodynamic implications were also investigated in relation to surface geological features, GPS velocities, absolute plate motion (APM), SKS/SKKS splitting, and other seismological observations. In addition to the fast polarization directions (FPDs) of the crustal anisotropy, we observed a conspicuous sharper clockwise rotation around the eastern Himalayan syntaxis than was revealed by GPS velocities. The distributed FPDs within and near the main active fault zones also favored the directions parallel to the faults. This implied that the deformation of a continuous medium revealed by GPS motions is a proxy for the deformation of the brittle shallow crust only, while the main active faults and the deep crustal interiors both play important roles in the deep deformation. Our results suggest that the deformation between the crust and upper mantle within the northernmost section of the Indochina block is decoupled due to the large difference in the directions between the observations related to the crust (GPS and crustal anisotropy) and mantle (APM and mantle anisotropy). Focusing on the transition zone between the plateau and the South China and Indochina blocks, we suggest that the motion of the Central Yunnan sub-block is a southeastward extrusion by way of tectonic escape. There is less deformation in the deep crust and the motion is controlled by the active boundary faults of the Ailaoshan-Red River shear zone to the west and the Xianshuihe-Xiaojiang fault to the east; the lower crustal flow within the plateau southeastward reached the Lijiang-Xiaojinhe fault, but further south it was obstructed by the Central Yunnan sub-block. © 2012 International Association for Gondwana Research. Source

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