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Zhou S.-H.,Institute of Earthquake Science | Jiang H.-K.,China Earthquake Networks Center
Earthquake | Year: 2016

This paper briefly introduces current progress in the field of foreshock research, both in China and abroad. We contrast common characteristics and the mechanism of foreshocks and foreshock sequence under the different definitions of foreshocks. Theoretically, cascade model or pre-slid model can explain foreshock. Foreshocks are mainly concentrated in the range of 10~75 km off the mainshock, but its time distribution form is very complicated, mostly 1 to 2 days before mainshock, the seismicity rate of part of foreshock sequences show significant acceleration features, but many foreshock sequences often show attenuation characteristics of mainshock-aftershock sequences. The most prominent feature of foreshocks is consistency of focal mechanism and low b value of earthquake sequence. Foreshocks seem to have a certain relationship with tectonic environment and the rupture form of mainshock, and in some cases, the dip-thrusting earthquakes seem to have relatively more foreshocks. Some earthquake cases show that focal depth of foreshocks gradually moves downward with the mainshock approaching. So far, it is difficult to determine whether an earthquake or an earthquake sequence is foreshock or foreshock sequence before earthquake, the identification method of foreshock mainly including statistical method of analogy, focal consistent mechanism and related derivative method, the fine detection of earthquake nucleation process. From the few existing studies of earthquake cases, in spite of temporal earthquake clusters and focal consistent mechanism are the most significant features of foreshock sequence, not sufficient condition for judgment foreshock sequence. Due to the rupture rate of expansion and sliding displacement have a tendency to increase faster over time, thus the method of the fine detection of earthquake nucleation process is expected to play a more important role in the identification of foreshock. © 2016, Science Press. All right reserved.

Zhang X.,Institute of Earthquake Science | Shen X.,Chinese Institute of Crustal Dynamics
Proceedings of the International Astronautical Congress, IAC | Year: 2016

Based on requirements of space technologies for protecting against and mitigating earthquake disasters, China Earthquake Adminstration (CEA) starts and carries out CSES mission, to develop the space-ground stereo earthquake monitoring system. The implement of this mission will be of great importance in earth observation system and earthquake/space weather early warning. For preventing and mitigating earthquake disasters, China is building the earthquake observation network both from ground and space, and the integrated stereo electromagnetic observing system are constructed and improved gradually, especially at seismic regions. 1. Chinese Seismo-Electromagnetic Satellites: The first Chinese seismo-electromagnetic satellite (CSES) is an experimental satellite with promising seismic applications. Its major scientific objectives are to monitor the space environment at topside ionosphere and global seismic activity, to provide space information for studying geosphere coupling mechanism. The scientific payloads installed are optical pumping magnetometer from Austria; fluxgate magnetometer; search-coil magnetometer; Electric field detector from Italy and China; Plasma Analyzer; Langmuir probe; GNSS occultation receiver; tri-band beacon transmitter; High energetic particle detectors cooperated with Italy. 2. Data product levels and key data processing techniques: The scientific data product are classified as four levels, level-0 is the raw data after processes of frame synchronization, descrambling, decoding; level-1 is the data after calibration and inversion; level-2 data is with the geometric correction; level-3 data is the time series from revisited orbits; level-4 is the spatial 2/3D distribution. Data analysis techniques aiming at different levels have been developed, in which calibration, and inversion methods are completed corresponding to different parameters. And also the CIT technique are developed by combing the multi-resource data from ground and satellite, including GNSS occultation, tri-band beacon, ground-based GPS TEC, vertical ionosonding and oblique sounding. 3. Stereo seismo-electromagnetic monitoring system: The ground-based electromagnetic monitoring networkhas been constructed for a long time period, including the observation on apparent resistivity, geoelectric field, geomagnetic field, electromagnetic emission, the GPS TEC network, vertical/oblique ionosounding, VLF radio wave receiver, and Schumann resonance. Combined with the satellite observation at topside ionosphere, a 3D dynamic observation network for seismo-electromagnetic information is built. Some kinds of data have been utilized in the same earthquake study, and the propagation coupling models are developed such as full-wave propagation model, acoustic gravity wave propagation model, etc.

Time series and characteristics of crustal deformation and coseismic displacement of the 2013 Minxian-Zhangxian MS6.6 Earthquake in Gansu province and its adjacent areas were obtained by high precision processing of CMONOC GPS data. The result indicates that only the GSMX of CMONOC fiducial stations in this area observed obvious coseismic displacement (about 18.7 mm), which means that the affected area of this earthquake is about 30~50 km from the epicenter, and the crustal movement in this area is active, regular and consistent. The velocity in the west is faster than in the east, the minimum (about 4.4 mm/a) is in the southeast and the maximum (about 18.4 mm/a) is in the southwest. The tectonic deformation in this area is mostly in compressed regime. © 2016, Science Press. All right reserved.

Dai Z.-H.,Institute of Earthquake Science | Zhang X.-D.,Institute of Earthquake Science
Earthquake | Year: 2016

In this paper, we extracted seismic velocity changes associated with the 2014 Ludian MS6.5 earthquake from ambient noise cross-correlation by using continuous seismic data recorded by 13 seismic stations in the research area. Base on temporal changes of seismic velocity of each seismic station pair, we got the spatial distribution of seismic velocity changes, and found that it has significant regional variation. The great changes are mainly distributed on the zones of Zemuhe fault, Xiaojiang fault and Lianfeng fault. There is a sudden post-seismic velocity drop for the region of the southwest segment of the Lianfeng fault and the northwest segment of the Zemuhe fault, and there is a sudden post-seismic velocity increase for the junctional zone of Zemuhe fault and Xiaojiang fault. We found that post-seismic velocity change and stress change have high consistency in the spatial distribution by comparing the stress accumulation of the main active faults around the Ludian earthquake. And there was a positive correlation between co-seismic velocity change and co-seismic stress change. Therefore, stress change associated with the Ludian earthquake may be the main reason of seismic velocity change. We extracted the co-seismic velocity changes associated with the MS5.1 Yongshan earthquake of April 5, 2014 by the same method. The result showed that seismic velocity increased in the source area of the Ludian earthquake after the Yongshan earthquake. © 2016, Science Press. All right reserved.

Feng W.,Institute of Earthquake Science | Feng W.,China Earthquake Networks Center
Earthquake | Year: 2016

For earthquake disaster mitigation, we use the records of more complete intensity data(from AD 1500 to 2015) on earthquake-prone area in the Yunnan area, and analyze earthquake intensity-frequency estimation. We digitized intensity observations and divided the cell size of 0.2°×0.2°, and calculated seismic intensity-frequency relationship for each cell. And combined with repeated cycle intensity of one hundred years and population economic data in Yunnan, we analyse future areas of concern. The results can provide reference for earthquake hazardous area zoning. This method is based on the historical earthquake data, reducing as far as possible the assessment of various hypotheses. It concisely reflects different frequency distribution of intensities. © 2016, Science Press. All right reserved.

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.

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.

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.

Gu G.-H.,Institute of Earthquake Science
Earthquake | Year: 2012

Progress in observation techniques, data processing techniques and software for crustal deformation observations and studies on earthquake precursors in the last decades is reviewed. Earthquake predictions in China have obtained rare successes but suffered more tragic failures since the Xintai earthquake in 1966, and have developed with twists and turns under the influence of the assertion that earthquakes are unpredictable and etc.. Though the 2008 M8.0 Wenchuan earthquake and the 2011 M9.0 East Japan earthquake were failed to predict, GPS observations before and after these two events and other events have shown that there were precursors to these events and large earthquakes are predictable. Features of different observation techniques, data processing methods are compared and some recent studies on precursory crustal deformations are summarized, so various advantages of GPS technique are emphasized. The facts show that anomalies or precursors detected from GPS observations before the great Wenchuan earthquake have been the most remarkable results of explorations in crustal movements and earthquake precursors in China.

Jiang Z.-S.,Institute of Earthquake Science | Wu Y.-Q.,Institute of Earthquake Science
Earthquake | Year: 2012

Based on the analysis of the preparation characteristics of the Kunlun 8.1 earthquake and the Wenchuan 8.0 earthquake revealed from GPS data, we review the main research developments of earthquake mechanism and forecast using crustal deformation data in the past decades, and discuss the similarities and differences of scientific approaches between Chinese and foreign scholars. Deformation characteristics of earthquake preparation associated with slip faults and dip-slip faults are analyzed. It is emphasized that, in order to understand the model of relationship between the crustal deformation and earthquake preparation, we should expand the attentions from fault scale to regional scale, and recognize the dynamic deformation characteristics associated with earthquake preparation in multi-scale, spatial-temporal process, and so to obtain the criteria of strong earthquake forecast.

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