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Qu W.,Changan University | Qu W.,University of Glasgow | Zhang Q.,Changan University | Zhang Q.,University of Glasgow | And 2 more authors.
Wuhan Daxue Xuebao (Xinxi Kexue Ban)/Geomatics and Information Science of Wuhan University

In order to visualize the detail motion among stations within the Shanxi graben, we build the No-Net-Rotation based on the GPS repeat observations from 1999 to 2007 of the crustal motion observation network in China. Then the spatial distribution feature of strain fields are analyzed by graphic element method, and the dynamic mechanism of crustal deformation is also deeply analyzed. The results show that present tectonic strain fields of Shanxi graben present tensile strain with NNW-SSE direction, which has good consistency with the earthquake focal mechanisms and regional long-term tectonic deformation background. And the present crustal movement of Linfen and Datong basin is strong, meanwhile, the Linfen and Datong basin is also the areas with high shear strain. In the end the reason of exceptive deformation area is discussed. Then we put forward a significant tectonic event that the crustal activities of tectonic uplift between the Linfen and Taiyuan basin is fierce, and the tectonic uplift is now undergo intense tension rupture. Source

Zhou C.,Institute of Geology | Zhou C.,The Second Monitoring and Application Center | Wang Q.-L.,Institute of Geology
Wuli Xuebao/Acta Physica Sinica

The nonlinear theory in Earth Science is very important for solving the problems of the earth. When considering some of the nonlinear properties of the medium, solitary wave (a special wave with a finite amplitude and a single peak or trough) may appear. Previous studies showed that it may be related to the rupture in the earthquake process. Therefore, it would be very helpful to explain some special phenomena in actual observation data if we fully understand the characteristics of nonlinear waves. In this paper, based on the nonlinear acoustic wave equation, we first perform 1-D nonlinear acoustic wave modeling in solid media using a staggered grid finite difference method. To get the stable and accurate results, a flux-corrected transport method is used. Then we analyze several different types of nonlinear acoustic waves by setting different parameters to investigate their nonlinear characteristics in the solid media. Compared with the linear wave propagation, our results show that the nonlinear coefficients have important influences on the propagation of the acoustic waves. When the equations contain only a third-order nonlinear term (consider the case β1≠0, β2 = 0, α = 0), the main lobe of the wave is tilted backward and its amplitude gradually attenuates with the wave spreading, and the amplitude of its front side-lobe attenuates slowly while the back side-lobe attenuates quickly. The whole shape and amplitude of the wave remain unchanged after propagating a certain distance. When the equations contain only a fourth-order nonlinear term (consider the case β2≠0, β1 = 0, α= 0), the main lobe and the two side-lobes of the wave are all slowly damped, but the shape of the whole wave is unchanged with the wave spreading. In addition, for some combinations of nonlinear and dispersive parameters (consider the case β1≠0, α≠0, β2 = 0), the wave acts like the linear wave, and the nonlinear acoustic wave is equal to solitary wave which is usually obtained by Kortewegde de Vries (KdV) equation. We validate our modeling method by comparing our results with the analytic solitary solutions. Solitary wave propagates with a fixed velocity slightly less than that of the linear compressional wave, which is probably due to the balance between nonlinear and dispersion effects, making the stress-strain constitutive relations show the nature of linear wave. © 2015, Chinese Physical Society. Source

Zhao Y.-F.,The Second Monitoring and Application Center | Zhu Y.-Q.,The Second Monitoring and Application Center | Zhu Y.-Q.,State Key Laboratory of Geodesy and Earths Dynamics | Liu F.,The Second Monitoring and Application Center
Dizhen Dizhi

In this paper, according to the synthetic gravity anomaly of a horizontally infinite cylindrical geologic body, gravity gradient in horizontal direction was calculated by potential field discrete cosine transformation in frequency domain. In the calculation, the minimum curvature method was used to extend edge lines. We found that the gravity gradient field from the potential field transformation was dependable by comparison with synthetic gravity gradient, except the data in the edges. Then, the accumulative horizontal gravity gradients before Lushan MS7.0 earthquake were calculated for the accumulative gravity anomaly from September 2010 to October 2012. In the north-south direction, gravity gradient in Daofu-Kangding-Shimian and Markang-Lixian-Lushan exhibited a positive high value, and the strike of the high value zone was in line with the strike of Xianshuihe Faults and Markang Faults. In the east-west direction, high value zone was not as obvious as that in the north-south direction. Gravity gradients in the direction along and vertical to the strike of Longmenshan Faults were calculated by the definition of directional derivative. In the along-strike direction, high gravity gradient values appeared in Markang-Lixian areas along Markang Faults and Daofu-Kangding-Shimian areas along Xianshuihe Faults, and extremum appeared in Kangding-Shimian and the area nearby Lixian. In the direction vertical to the strike of Longmenshan fault zone, high gravity gradient values appeared in Lixian-Lushan-Kangding-Shimian areas, and the extremum appeared in the area nearby Kangding. The results indicate that gravity gradient in the direction along and vertical to the strike of faults can better show the relative gravity change on the two sides of faults. Lushan MS7.0 earthquake is located at the transition zone between the two high value zones of gravity gradient. The total horizontal gravity gradient shows that the location and strike of the high value zone are basically consistent with regional faults, and the extremums of total horizontal gravity gradient appeared nearby Lixian, Kangding and Shimian. © 2015, Editorial Office of Seismology and Geology. All right reserved. Source

Zhang X.,The Second Monitoring and Application Center | Li R.,The Second Monitoring and Application Center | Jia P.,The Second Monitoring and Application Center | Wang Q.,The Second Monitoring and Application Center
Wuhan Daxue Xuebao (Xinxi Kexue Ban)/Geomatics and Information Science of Wuhan University

We use disturbance abnormity with features of precursor wave from pointing-precursor observation of epicenter area and nearby within hundreds kilometers in Qinghai-Sichuan area before the Wenchuan Ms 8.0 earthquake on May 12, 2008 to search possible epicenter-source area. According to its abnormity vector, extent, time, space-location and the distribution characteristics of tectonic fracture, aided by construction of source-spreading function and inversion of quasi-Newton least square method. Computed epicenter-source is located on the northern segment of Longmenshan fracture, about 134 km away from real epicenter, occurred nearly 13 hours before this earthquake. Source

Zhang X.,The Second Monitoring and Application Center | Tang H.,The Second Monitoring and Application Center | Jia P.,The Second Monitoring and Application Center | Gong S.,The Second Monitoring and Application Center
Wuhan Daxue Xuebao (Xinxi Kexue Ban)/Geomatics and Information Science of Wuhan University

Using 5 typical observational curve at sites such as Shihuiyaokou, Hongliuxia, Wozitan, Biandukou and Nanying, in the monitoring area of Gansu Province and its boundaries with Ningxia and Qinghai Provinces, the slow time-varying precursor system is constructed, the abnormity is identified, and the possible relationship between the abnormity and preparation of earthquakes around or over 6.0 magnitude are researched. The results show that at the medium and short-term phase before these earthquakes, the maximum module of latent root exceeded 1.0. This method reduced factitious or experiential identification of abnormity relative to analysis of observational curve, also reflects dynamic variation and adaptive features of precursor system structure for cross-fault deformation. Source

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