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Nilupar T.,Institute of Earthquake Science | Zhang Y.-X.,China Earthquake Networks Center
Earthquake | Year: 2012

In this paper, we review recent advances and latest developments on the study of ionospheric disturbances prior to earthquakes. We also introduce DEMETER satellite and some statistical studies and earthquake case studies based on DEMETER satellite data. The common steps for studying ionospheric phenomena before strong earthquakes are expounded: select the earthquake examples-choose the parameters of the ionosphere-data analysis, extract and identify disturbance information-validate pre-earthquake ionospheric responses. The electromagnetic effects and correlated phenomena generated in seismo-electromagnetic process, spread to space by ways of chemistry, acoustics, and electromagnetism. The research results show clearly that ionospheric disturbances appearing several months, days or hours prior to earthquakes can be observed. Whether the precursors could be used as a tool in earthquake prediction need more research.

Based on spatial distribution and characteristics of seismic migration after the earthquakes in the northwest region of the the Tibet plateau, we discussed the main active tectonic structures and seismic activity, which related to seismic migration. By analyzing the relationship between active tectonics and seismic activity, the following conclusion-sareobtained: (1) Migration earthquakes are unevenly distributed in the border of active blocks, controlled by the large active tectonic zones; (2) There are three migration paths, dominated by the second path; (3) Within the next five years in the west area of the Altun fault zone, there will be one or two earthquakes of magnitude 6.5; (4) Earthquakes happened after 1900 are mainly distributed along the empty areas; (5) Within the next three to six months, strong migration earthquakes may occur in seismic empty areas, such as the south section of Longmenshan.

Yan R.,A+ Network | Jiang C.-S.,Institute of Geophysics | Zhang L.-P.,Institute of Earthquake Science
Chinese Journal of Geophysics (Acta Geophysica Sinica) | Year: 2011

In recent years, critical slowing down phenomenon have shown great potentials on the aspects of disclosing whether or not a complex dynamic system is tend to critical cataclysm. Based on the concepts of critical slowing down, the observed data of radon concentrations in water were processed in this article. Take radon concentration observation data at Longmen Mountain fault zone and nearby regions before the Wenchuan Ms8. 0 earthquake on May 12, 2008 as an example, the autocorrelation coefficients and variances which can characterize critical slowing down have been calculated separately. The result indicated that radon data at different station had obviously critical slowing down phenomenon before the Wenchuan Ms8. 0 earthquake, which indicated that critical slowing down phenomenon is a possible early warning signal for strong earthquakes. The introduction and study on critical slowing down theory into precursory data processing have practical significances and important scientific values to thoroughly understand precursor mechanism, to determine the stage of precursory anomalies and to enhance earthquake prediction level.

Shao Z.-G.,Institute of Earthquake Science | Zhou L.-Q.,China Earthquake Networks Center | Jiang C.-S.,Institute of Geophysics | Ma H.-S.,Institute of Earthquake Science | Zhang L.-P.,Institute of Earthquake Science
Chinese Journal of Geophysics (Acta Geophysica Sinica) | Year: 2010

In order to analyze the effect of Wenchuan Ms8.0 earthquake on the seismic activity of surrounding faults, we calculate the dynamic changes of Coulomb stress caused by the Wenchuan Ms8.0 earthquake with a Burgers viscous relaxation model. Simulation result shows significant increase of Coulomb stress on four majors fault segments, which are Daofu-Kangding section in the Xianshuihe fault, Maqu section in the East Kunlun fault, the southern section of the Longmen Shan fault, and the Qingchuan fault respectively. Furthermore, the Coulomb stress change caused by the post-seismic relaxation during 4 years after Wenchuan Ms8.0 earthquake is so strong that it almost matches to that caused by the co-seismic rupture. That is to say, the effect of the postseismic relaxation is nearly equal to that caused by the Wenchuan earthquake itself. This is a strong evidence that the postseismic relaxation is critically important so it should not be neglected on evaluating the effects of strong earthquake. Taking the postseismic effect into consideration, the probability of seismicity is evaluated by the Dieterich (1994) model based on the dynamic evolution of Coulomb stress and the background seismic rate. Combining the relevant structural geology, historical earthquake, aftershocks activities and some other minor factors, a comprehensive analysis shows that the seismic hazards on the above four fault segments are ranked from high to low as Daofu-Kangding section in Xianshuihe fault, the southern section of the Longmen Shan fault, the Maqu section in East Kunlun fault and the Qingchuan fault.

Wu Y.,Institute of Geology | Wu Y.,Institute of Earthquake Science | Jiang Z.,Institute of Earthquake Science | Yang G.,First Crust Deformation Monitoring and Application Center | And 3 more authors.
Geophysical Journal International | Year: 2011

Using modelled and simulated data for comparison of several methods to compute GPS strain rate fields in terms of their precision and robustness reveals that least-squares collocation is superior. Large scale (75°E-135°E and 20°N-50°N) analyses of 1° grid sampling data and decimated 50 per cent data by resampling (then erasing data in two 5°× 10° region) reveal that the Delaunay method has poor performance and that the other three methods show high accuracy. The correlation coefficients between theoretical results and calculated results obtained with different errors in input data show that the order in terms of robustness, from good to bad, is least-squares collocation, spherical harmonics, multisurface function and the Delaunay method. The influence of data sparseness on different methods shows that least-squares collocation is better than spherical harmonics and multisurface function when sample data are distributed from a 2° grid to a 1° grid. Analysis to medium scale (90°E-120°E, 25°N-40°N) in 1°-0.5° grid sampling data reveals that least-squares collocation is superior to other methods in terms of robustness and sensitivity to data sparseness, but their difference is slight. Strain rate results obtained for the Chinese mainland using GPS data from 1999 to 2004 show that the spherical harmonics method has edge effects and that its value and range increase concomitantly with increased sparseness. The multisurface function method shows non-steady-state characteristics; the errors of results increase concomitantly with increased sparseness. The least-squares collocation method shows steady characteristics. The errors of results show no significant increase even though 50 per cent of input data are decimated by resampling. The spherical harmonics and multisurface function methods are affected by the geometric distribution of input data, but the least-squares collocation method is not. © 2011 The Authors Geophysical Journal International © 2011 RAS.

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