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Tan K.,China Earthquake Administration | Zhang C.,China Earthquake Administration | Zhao B.,China Earthquake Administration | Wang Q.,Wuhan University | And 4 more authors.
Geodesy and Geodynamics | Year: 2017

The equivalence of geophysical fields, the finiteness of measurements and the measurement errors make the result of geophysical inversion non-unique. For example, the measurements and inversion method used, the priori rupture model determined and the slip distribution smoothing factor selected will have significant influences on the earthquake rupture slip distribution. Using different data and methods, different authors have given different rupture slip distribution models of the 2015 Mw7.9 Nepal earthquake, with the maximum slip ranging from 3.0 m to 6.8 m. In this paper, geometry parameters of the single rectangular fault model in elastic half-space were inferred constraining with the Global Positioning System (GPS) and Interferometric Synthetic Aperture Radar (InSAR) coseismic deformations and bounding the slip with approximate average value; and then, the single rectangular fault was divided into multiple sub-faults, and the final slip smoothing factor, the final slip distribution and the maximum slip were determined with the misfit-roughness tradeoff curve, the cross-validation sum of squares (CVSS) and the third-party observation data or indexes being comprehensively taken into account. The results show that, the rupture of the Nepal earthquake extended by over 100 km east by south. The maximum slip of the earthquake was about 6.5-6.7 m, and most of the slip is confined at depths of 8-20 km, consistent with the depth distribution of aftershocks. The method for reducing the multiplicity of solutions to rupture slip distribution in this paper was ever used in inversion of rupture slip distribution for the 2008 Wenchuan and 2013 Lushan earthquakes, and the third-party measurement - surface dislocation has very large effect on reducing the multiplicity of solutions to inversion of the Wenchuan earthquake. Other priori information or indicators, such as fault strike, dip, earthquake magnitude, seismic activity, Coulomb stress, and seismic period, can be used for beneficial validation of and comparison with inversion results. © 2017 The Authors.

Wang X.-S.,National Earthquake Infrastructure Service | Han Y.-F.,National Earthquake Infrastructure Service | Xu W.-M.,Institute of Geophysics
Earthquake | Year: 2016

We carried a research on main frequency characteristics of gravity disturbance signals before Yutian Ms7.3, Ludian Ms6.5, Jinggu Ms6.6 and Pishan Ms6.5 earthquakes, as well as gravity disturbance signals induced by typhoon 'Huangfeng', 'Weimaxun', and 'Maidemu', based on continuous gravity observations from Crustal Movement Observation Network of China (CMONOC). The results show that the gravity disturbance signals before earthquake and induced by typhoon cannot be distinguished with its main frequency which is similar and all correspond to 4~7 s. The range and standard deviation of gravity disturbance signals before earthquake are both lower than 0.02 Hz without any influence of typhoon, in contrast, they are both higer than 0.02 Hz when it is induced by typhoon. The range and standard deviation of main frequency can be used to separate the gravity disturbance signals before earthquake from typhoon effect. This work will greatly improve the applications of the continuous gravity observations in earthquake short-term monitoring. © 2016, Science Press. All right reserved.

Ma H.-J.,National Earthquake Infrastructure Service | Lu N.,Peking University | Li X.-X.,National Earthquake Infrastructure Service
Earthquake | Year: 2013

Roads are the traffic lifeline for emergency rescue and disaster relief. After huge earthquakes, it is very important to rapidly extract road damages from remote sensing images for disaster emergency rescue. However, because damages caused by earthquakes is different at different places, it is very complicated to extract in a common way. Usually, spectral features are used to discriminate damaged and undamaged pixels or objects in images. Because thresholds have to be chosen by manual operation dependent on different situations, methods based on spectral features are low in accuracy and efficiency. This paper proposes an approach to rapidly extract road damages by earthquake based on sidelines. The approach extracts double sidelines of undamaged road from images acquired after earthquakes, and then compare them with vector road lines before earthquakes. The damaged segments of roads can be extracted through comparison. The performance of the method is evaluated by an experiment with QuickBird images in the disaster area of the 2008 Wenchuan earthquake.

Tu J.,Harbin Institute of Technology | Liu H.,National Earthquake Infrastructure Service | Tang A.,Harbin Institute of Technology | Zheng T.,China Earthquake Administration
Yanshilixue Yu Gongcheng Xuebao/Chinese Journal of Rock Mechanics and Engineering | Year: 2015

The acceleration response can be used to analyze the mechanisms of a landslide and to determine the coefficients of earthquake influence reasonably. The centrifuge shaking table test of 50g modelling the colluvial landslide was carried out. The landslide model was placed in a rigid aluminum alloy container with the length of 600 mm, width of 400 mm and height of 500 mm. The bedrock wave recorded at Qingxi station during the Wenchuan earthquake was exerted from the bottom of the model. The amplification coefficients of the horizontal and vertical peak ground acceleration(PGA) at landslide surface were found to increase with the increasing of the elevation. The increasing rate of the amplification coefficients of PGA at the measured spots near the slope crest was notably larger. The acceleration response at the slope surface was significantly different from that inside the landslide. The horizontal acceleration at bedrock had the amplification effect along the elevation of the landslide, but was much smaller than that at the landslide surface. A phenomenon of wave mode transformation was found at the crest of the landslide. The amplification coefficients of PGA at the crest of landslide increased firstly and subsequently decreased with the increasing of the amplitudes of the input seismic wave. ©, 2015, Academia Sinica. All right reserved.

Tu J.,Harbin Institute of Technology | Liu H.,National Earthquake Infrastructure Service | Tang A.,Harbin Institute of Technology | Zheng T.,China Earthquake Administration
Yanshilixue Yu Gongcheng Xuebao/Chinese Journal of Rock Mechanics and Engineering | Year: 2016

Centrifuge shaking table model test of colluvial landslide reinforced by cantilever anti-slide pile was designed and carried out on a centrifuge shaking table at 50 gravitational accelerations in order to research its seismic response, the distribution regularity of dynamic soil pressure after pile and dynamic bending moment of the anti-slide pile. During the processing of the model test, bedrock wave(Qingxi wave) was inputted from the bottom of the model by scaling the amplitude of the input seismic wave. The seismic performance of colluvial landslide reinforced by cantilever anti-slide pile under earthquakes of different intensities is studied by monitoring the acceleration response of landslide at different positions, the dynamic soil pressure after pile and the strain of the anti-slide pile. Results show that the acceleration response of landslide increases with the increasing height of landslide. The landslide shows an obvious elevation amplification effect, i.e., the increasing rate of the peak ground acceleration(PGA) amplification coefficients becomes notably larger approaching the slope crest, and the acceleration response characteristic of the landslide surface shows the surface effect under earthquake. The dynamic response of the soil is restricted by anti-slide pile to a certain degree. The dynamic soil pressures after pile rapidly increase to peak value and then keep roughly stable along with the excitation of earthquake motion. And they will form dynamic soil pressures to act on the anti-slide pile. The maximum dynamic bending moment of the pile appears near the bedrock surface, which the distribution rule reflects the convex form. Both the dynamic soil pressure after pile and dynamic bending moment of the pile will increase with the increasing the strength of seismic wave. The results provide a good foundation for seismic design of the cantilever anti-slide pile. © 2016, Science Press. All right reserved.

Xiang L.,CAS Wuhan Institute of Geodesy and Geophysics | Xiang L.,University of Chinese Academy of Sciences | Wang H.,CAS Wuhan Institute of Geodesy and Geophysics | Steffen H.,Lantmateriet | And 4 more authors.
Earth and Planetary Science Letters | Year: 2016

Understanding groundwater storage (GWS) changes is vital to the utilization and control of water resources in the Tibetan Plateau. However, well level observations are rare in this big area, and reliable hydrology models including GWS are not available. We use hydro-geodesy to quantitate GWS changes in the Tibetan Plateau and surroundings from 2003 to 2009 using a combined analysis of satellite gravity and satellite altimetry data, hydrology models as well as a model of glacial isostatic adjustment (GIA). Release-5 GRACE gravity data are jointly used in a mascon fitting method to estimate the terrestrial water storage (TWS) changes during the period, from which the hydrology contributions and the GIA effects are effectively deducted to give the estimates of GWS changes for 12 selected regions of interest. The hydrology contributions are carefully calculated from glaciers and lakes by ICESat-1 satellite altimetry data, permafrost degradation by an Active-Layer Depth (ALD) model, soil moisture and snow water equivalent by multiple hydrology models, and the GIA effects are calculated with the new ICE-6G_C (VM5a) model. Taking into account the measurement errors and the variability of the models, the uncertainties are rigorously estimated for the TWS changes, the hydrology contributions (including GWS changes) and the GIA effect. For the first time, we show explicitly separated GWS changes in the Tibetan Plateau and adjacent areas except for those to the south of the Himalayas. We find increasing trend rates for eight basins: [Formula presented] for the Jinsha River basin, [Formula presented] for the Nujiang-Lancangjiang Rivers Source Region, [Formula presented] for the Yangtze River Source Region, [Formula presented] for the Yellow River Source Region, [Formula presented] for the Qaidam basin, [Formula presented] for the central Qiangtang Nature Reserve, [Formula presented] for the Upper Indus basin and [Formula presented] for the Aksu River basin. All these increasing trends are most likely caused by increased runoff recharges from melt water and/or precipitation in the surroundings. We also find that the administrative actions such as the Chinese Ecological Protection and Construction Project help to store more groundwater in the Three Rivers Source Region, and suggest that seepages from the Endorheic basin to the west of it are a possible source for GWS increase in this region. In addition, our estimates for GWS changes basically confirm previous results along Afghanistan, Pakistan, north India and Bangladesh, and clearly reflect the excessive use of groundwater. Our results will benefit the water resource management in the study area, and are of particular significance for the ecological restoration in the Tibetan Plateau. © 2016 The Author(s)

Liu Y.,China Earthquake Administration | Zhao J.,National Earthquake Infrastructure Service | Liu P.,National Earthquake Infrastructure Service
Journal of Natural Disasters | Year: 2015

In this paper, Chuanqing block and its surrounding three main active faults, including Xianshuihe fracture zone, Longmenshan fracture zone and Dongkunlun fracture zone, were taken as research object. Based on data for tectonic stress field, GPS monitsring, geology historical earthguaks, and state-related friction canstitutive relation. The mechanics and motion states of faults - blocks before and after the recent destructive earthquakes-Kunlunshan earthquake, Wenchuan earthquake, Yushu earthquake and Lushan earthquake were simulated. The results show that there are relations between stress, strain, displacement states and earthquake. Strong earthquakes may happen in Ganzhi-Daofu segment of Xianshuihe fracture zone, southwest and northeast segments of Longmenshan fracture zone in the future according to preliminary inference.

Wang M.,China Earthquake Administration | Lou W.,China Earthquake Administration | Li P.,China Earthquake Administration | Li P.,Institute of Earth quake Science | And 2 more authors.
Journal of Atmospheric and Solar-Terrestrial Physics | Year: 2013

A major geomagnetic storm occurred on July 15-16, 2012, which is characterized by a long-lasting southward turning of interplanetary geomagnetic field (IMF) for ~30. h below -10. nT. Prominent large-scale ionospheric disturbances were observed in North China during this extreme space weather event. This study reveals the possibility of using the newly built China seismo-ionospheric ground-based monitoring network (CSGMN) to investigate the ionospheric storm effect during different phase of the storm. As a main part of the CSGMN, the oblique and vertical sounding systems and global position system (GPS) network all observed a moderate and a strong positive storm effects around the noon and the sunset sector on 15 July. The maximum enhancement of parameter peak electron density (NmF2) increased 100% and TEC 60%. The positive phase then is followed by an intense negative storm effect during the entire day on July 16 with NmF2 and TEC fell below 40% of the previous quiet day values. Also, the electron density profiles retrieved from the COSMIC radio occultation measurements were examined and validated with the ground measurements in order to estimate the possibility of its use as an additional data source to study altitude distribution of ionospheric storms. Good agreement has been reached between the ground and satellite occultation measurements even if they are not close. The result here shows that CSGMN can be a very powerful network not only for the seismo-ionospheric study but also in monitoring space weather. © 2013 .

Li X.-X.,National Earthquake Infrastructure Service | Ma H.-J.,National Earthquake Infrastructure Service
Earthquake | Year: 2013

Earthquake-induced collapses and slides are one of the geological disasters that can seriously endanger human life after earthquakes. In this article we select as study area the heavily devastated area Wenchuan county in the 2008 Wenchuan earthquake. Risk assessment of earthquake-induced collapses and slides is based on remote sensing data and GIS method, combined with the geological environment background of the study area. Logistic regression model was selected and the study area is ultimately categorized into five classes, namely, not dangerous, slightly dangerous, dangerous, more dangerous, extremely dangerous.

Wang X.,National Earthquake Infrastructure Service | Wang X.,CAS Wuhan Institute of Geodesy and Geophysics | Fang J.,CAS Wuhan Institute of Geodesy and Geophysics | Hsu H.,CAS Wuhan Institute of Geodesy and Geophysics
Tectonophysics | Year: 2014

The lithosphere beneath the North China Craton (NCC) has been thinning since the Phanerozoic. Previous geophysical studies on NCC structures have mainly focused on the results of seismic wave propagation. In this study, we obtained 3D density structures of the NCC lithosphere by using the sequential inversion of observed gravity data and P-wave travel times. Analyses of the resulting density model and discussions of the destruction of the NCC are provided. Our density model shows that distinct horizontal and vertical density heterogeneities exist throughout the lithosphere beneath the NCC; in the west of the craton, the Ordos block is characterised by a relatively uniform high-density lithospheric mantle, while laterally heterogeneous densities are observed at shallower than 100. km depth. Distinct low-density anomalies are imaged in the Cenozoic Yinchuan-Hetao and Shaanxi-Shanxi rifts surrounding the Ordos block. Comparing with the thinned lithosphere and high Poisson's ratio, the low density in the rifts may indicate partial melting induced by thermo-mechanical erosion. Predominantly low-density anomalies, which represent an upwelling of the asthenosphere, are revealed in the south of the Taihang orogen, as well as at the junction of the Yinshan-Yanshan orogen (near Datong volcano) and the Taihangshan orogen, from 100 to 200. km depth. This supports the hypothesis of thermo-mechanical erosion in these regions. High-density anomalies are visible at the base of the lithosphere or in the upper mantle beneath the central North China Basin. Combined with high velocities at 300. km depth indicated by seismic tomography, these high densities suggest that the lithospheric destruction of this region may not be explained by thermo-mechanical erosion, as there is no evidence of deep, hot upwelling that could support thermo-mechanical erosion. © 2014 Elsevier B.V.

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