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Li R.,China Earthquake Administration | Tang J.,China Earthquake Administration | Tang J.,State Key Laboratory of Earthquake Dynamics | Dong Z.-Y.,China Earthquake Administration | And 4 more authors.
Chinese Journal of Geophysics (Acta Geophysica Sinica) | Year: 2014

Magnetotelluric sounding profile was carried out at 114 sites from northeast to southwest in the southern area of Yunnan Province for the exploration of seismogenic environment in deep earth. An electrical structure model of crust and upper mantle was obtained after Robust processing, Qualitative Analysis and two dimension inversion of the observation data. Three strong earthquake belts are distributed along the profile. The deep seismogenic structure shows that: (1) the electrical structure of crust and upper mantle along the profile is broadly consistent with the regional geological data; (2) all of the strong earthquake belts along the profile from Menglian to Luoping have low resistance area and resistivity gradient zone; (3) resistivity difference between two sides of deep fault is the important background of strong earthquake belts.

Zhu H.,State Key Laboratory of Earthquake Dynamics | Zhu H.,China Earthquake Administration | Wen X.,State Key Laboratory of Earthquake Dynamics | Wen X.,China Earthquake Administration
Journal of Earth Science | Year: 2010

In this article, firstly, we calculated and analyzed the patterns of Coulomb stress changes induced by a sequence of strong earthquakes that occurred in Songpan (Chinese Source), Sichuan (Chinese Source) Province in 1973 and 1976, and discovered that the Ms8.0 Wenchuan (Chinese Source) earthquake of 2008 was epicentered in a relevant Coulomb stress triggering zone. This suggests that the Coulomb stress on the middle and southern segments of the Longmenshan (Chinese Source) fault zone increased after the Songpan sequence of strong earthquakes, and the stress increment might cause the 2008 Wenchuan earthquake having already occurred somewhat ahead of time. Further, we calculated and analyzed Coulomb stress changes coinduced by both the Songpan sequence and the Ms8.0 Wenchuan mainshock. The result shows that the Ms6.4 Qingchuan (Chinese Source) earthquake of May 25, 2008 on the northeastern segment of the Longmenshan fault zone was triggered by the Wenchuan mainshock, and that the southwestern segment of the fault zone is also in the stress triggering zone. Besides, the Maoxian (Chinese Source)-Wenchuan fault (i.e., the back-range fault of the Longmenshan fault zone), which extends parallel to the seismogenic fault of the Wenchuan earthquake, is in a shadow zone of the Coulomb stress changes, and therefore, its potential hazard for producing a strong or large earthquake in the near future could be reduced relatively. © China University of Geosciences and Springer-Verlag Berlin Heidelberg 2010.

Yang C.,Shandong Institute of Earthquake Engineering | Yang C.,China Earthquake Administration | Yang C.,State Key Laboratory of Earthquake Dynamics | Cai W.,Shandong Institute of Earthquake Engineering | And 3 more authors.
Procedia Engineering | Year: 2012

Dynamic soil modulus and damping ratio are the two basic parameters to describe dynamic deformation characteristics of the soil. There are three ways to obtain soil dynamics parameters i.e. field test, laboratory test, and calculating empirical. Silt loam samples were collected from Dongying area in this study. In order to get the maximum dynamic shear modulus, the following methods were adopted. The shear wave velocity was tested in field using single-hole method, and the maximum dynamic shear modulus capacity was obtained based on the calculation result of the shear wave velocity. The paper compared the results obtained by three methods and got some useful conclusions. The maximum dynamic shear modulus value calculated by field test was close to the corresponding value from the laboratory dynamic triaxial test, while the value obtained from the empirical formula was significantly lower. However, as the theory, method and collation of data for two kinds of tests were different, their test results were not exactly the same. © 2012 Published by Elsevier Ltd.

Cheng H.H.,Chinese Academy of Sciences | Cheng H.H.,University of Chinese Academy of Sciences | Zhang H.,Chinese Academy of Sciences | Zhang H.,University of Chinese Academy of Sciences | And 12 more authors.
Science China Earth Sciences | Year: 2012

Coulomb failure stress changes (ΔCFS) are used in the study of reservoir-induced seismicity (RIS) generation. The threshold value of ΔCFS that can trigger earthquakes is an important issue that deserves thorough research. The Ms6. 1 earthquake in the Xinfengjiang Reservoir in 1962 is well acknowledged as the largest reservoir-induced earthquake in China. Therefore, it is a logical site for quantitative calculation of ΔCFS induced by the filling of the reservoir and for investigating the magnitude of ΔCFS that can trigger reservoir seismic activities. To better understand the RIS mechanism, a three-dimensional poroelastic finite element model of the Xinfengjiang Reservoir is proposed here, taking into consideration of the precise topography and dynamic water level. We calculate the instant changes of stress and pore pressure induced by water load, and the time variation of effective stresses due to pore water diffusion. The ΔCFS on the seismogenesis faults and the accumulation of strain energy in the reservoir region are also calculated. Primary results suggest that the reservoir impoundment increases both pore pressure and ΔCFS on the fault at the focal depth. The diffusion of pore pressure was likely the main factor that triggered the main earthquake, whereas the elastic stress owing to water load was relatively small. The magnitude of ΔCFS on seismogenesis fault can reach approximately 10 kPa, and the ΔCFS values at the hypocenter can be about 0. 7-3. 0 kPa, depending on the fault diffusion coefficient. The calculated maximum vertical subsidence caused by the water load in the Xinfengjiang Reservoir is 17. 5 mm, which is in good agreement with the observed value of 15 mm. The accumulated strain energy owing to water load was only about 7. 3×1011 J, even less than 1% of the seismic wave energy released by the earthquake. The reservoir impoundment was the only factor that triggered the earthquake. © 2012 Science China Press and Springer-Verlag Berlin Heidelberg.

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