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Yang D.,CAS Institute of Geology and Geophysics | Yang D.,Chinese Institute of Crustal Dynamics | Zeng R.,Chinese Institute of Crustal Dynamics | Zhang D.,CAS Institute of Mechanics
International Journal of Greenhouse Gas Control | Year: 2011

In this paper, inertial effects, mass interface and mass transfer mechanism are taken into account. By applying an updated space and time conservation element and solution element (CE/SE) method and hybrid particle level-set method, the stability simulation of the density-driven convection in deep saline aquifers is presented for short-term storage of CO2. The mass transfer equations coupled with two phase fluid flow equations are solved numerically to investigate effects of CO2 dissolution into brine on migration. Results show that Taylor instability phenomenon has been observed in CO2 storage in saline aquifers for short time scales, which contributes to the further dissolution of CO2 in saline aquifers. Density-driven convection dominates hydrodynamic trapping, while dissolution process of CO2 also has a great influence on CO2 sequestration. © 2010 Elsevier Ltd.

Chen Y.,CAS Institute of Geology and Geophysics | Zhang Z.,CAS Institute of Geology and Geophysics | Sun C.,Chinese Institute of Crustal Dynamics | Badal J.,University of Zaragoza
Gondwana Research | Year: 2013

In addition to crustal thickening, distinctly different mechanisms have been suggested to accommodate the huge convergences caused by the continental collision between India and Eurasia. As the transition zone between the two grand tectonic domains of Asia, the Tethys and the Pacific, east Tibet and its surrounding regions are the ideal places to study continental deformation. Pervasive rock deformation may produce anisotropy on the scale of seismic wavelengths; thus, seismic anisotropy provides insight into the deformation of the crust and mantle beneath tectonically active domains. In this study, we calculated receiver function pairs of radial- and transverse-components at 98 stations located in Sichuan and Yunnan provinces, China. We selected 7423 pairs with high signal-to-noise ratio (SNR) and unambiguous Moho converted Ps phases (Pms) to measure the Pms splitting owing to the crustal anisotropy. Both the crustal thickness and the average crustal Vp/Vs ratio were calculated simultaneously by the H. k stacking method. The geodynamic implications were also investigated in relation to surface geological features, GPS velocities, absolute plate motion (APM), SKS/SKKS splitting, and other seismological observations. In addition to the fast polarization directions (FPDs) of the crustal anisotropy, we observed a conspicuous sharper clockwise rotation around the eastern Himalayan syntaxis than was revealed by GPS velocities. The distributed FPDs within and near the main active fault zones also favored the directions parallel to the faults. This implied that the deformation of a continuous medium revealed by GPS motions is a proxy for the deformation of the brittle shallow crust only, while the main active faults and the deep crustal interiors both play important roles in the deep deformation. Our results suggest that the deformation between the crust and upper mantle within the northernmost section of the Indochina block is decoupled due to the large difference in the directions between the observations related to the crust (GPS and crustal anisotropy) and mantle (APM and mantle anisotropy). Focusing on the transition zone between the plateau and the South China and Indochina blocks, we suggest that the motion of the Central Yunnan sub-block is a southeastward extrusion by way of tectonic escape. There is less deformation in the deep crust and the motion is controlled by the active boundary faults of the Ailaoshan-Red River shear zone to the west and the Xianshuihe-Xiaojiang fault to the east; the lower crustal flow within the plateau southeastward reached the Lijiang-Xiaojinhe fault, but further south it was obstructed by the Central Yunnan sub-block. © 2012 International Association for Gondwana Research.

Tian Y.,Chinese Institute of Crustal Dynamics | Shen Z.-K.,University of California at Los Angeles
Journal of Geophysical Research B: Solid Earth | Year: 2016

We develop a spatial filtering method to remove random noise and extract the spatially correlated transients (i.e., common-mode component (CMC)) that deviate from zero mean over the span of detrended position time series of a continuous Global Positioning System (CGPS) network. The technique utilizes a weighting scheme that incorporates two factors-distances between neighboring sites and their correlations of long-term residual position time series. We use a grid search algorithm to find the optimal thresholds for deriving the CMC that minimizes the root-mean-square (RMS) of the filtered residual position time series. Comparing to the principal component analysis technique, our method achieves better (>13% on average) reduction of residual position scatters for the CGPS stations in western North America, eliminating regional transients of all spatial scales. It also has advantages in data manipulation: less intervention and applicable to a dense network of any spatial extent. Our method can also be used to detect CMC irrespective of its origins (i.e., tectonic or nontectonic), if such signals are of particular interests for further study. By varying the filtering distance range, the long-range CMC related to atmospheric disturbance can be filtered out, uncovering CMC associated with transient tectonic deformation. ©2016. The Authors.

Yang D.,Chinese Institute of Crustal Dynamics | Wang S.,CAS Institute of Geology and Geophysics | Zhang Y.,Japan Research Institute of Innovative Technology for the Earth
Aerosol and Air Quality Research | Year: 2014

Carbon dioxide (CO2) geological storage in deep saline aquifers is a key measure to mitigate global warming. However, it still faces a variety of technical challenges such as enhancing CO2 effective storage capacities. In this paper, a preliminary model is developed to simulate CO2 migration during nanofluid-based supercritical CO2 geological storage in saline aquifers. The main mechanisms, including Brownian motion, thermophoresis, thermal energy transfer, and interfacial tension, are included in the proposed conceptual model. Based on the high-resolution space-time conservation element and solution element (CE/SE) method, the model is used to simulate CO2 migration and distribution in the in-situ heterogeneous saline aquifer. It can be inferred that the involvement of nanoparticles decreases shear stresses opposing flow and enhances CO2 mobility in the flow boundary layer. In addition, nanoparticles increase shear stresses outside the boundary layer and retard CO2 velocity. These competitive mechanisms result in homogeneous migration of CO2 in the saline formation. One preliminary suggestion is that nanofluids enhance homogeneous CO2 transport in the reservoir and mitigate the negative effects of stratigraphic heterogeneity on migration and accumulation of the CO2 plume. CO2 effective storage capacity may be greatly elevated by means of nanofluid-based CO2 geological sequestration. The concept of nanofluid-based CO2 geological storage may be potentially conducive to large-scale commercial CO2 geological storage and useful for exploration of geothermal resources in deep-seated hot rocks. The effects of CO2 solubility and geochemical reactions on nanofluid flows may be considered in a future study. © Taiwan Association for Aerosol Research.

Qiu Z.-H.,Chinese Institute of Crustal Dynamics | Chi S.-L.,Hebi Seismological Bureau
Earthquake | Year: 2013

While a traditional seismograph records the variations of displacement with time at a point, a tensor strainmeter monitors the variations of the spacial gradient of displacement. An YRY-4 borehole strainmeter at Guza, Sichuan province, recorded three local seismic events at the sampling rate of 100 sps for the first time. At this high sampling rate, the data of the YRY-4 demonstrated a satisfying degree of self-consistency and sufficiently high credibility. The observation shows that P wave strain contains areal strain components as well as shear strain component. It gives direct evidence for the property of P wave. According to the theory of seismology, P wave is clarified to have no rotation, but it has volumetric strain and shear strains.

Zhang Y.,China Railway No.5 Engineering Group Co. | Xing B.,Beijing University of Technology | Song C.,Chinese Institute of Crustal Dynamics
Modern Tunnelling Technology | Year: 2014

Affected by staged excavation, stress-strain nonlinear variation may occur inside the surrounding rock of a tunnel. In high-ground-stress areas, this mechanical effect tends to be even more obvious and can cause serious geological disasters like rockbursts and wall caving, etc. Taking the construction of the Meihuashan tunnel in Fujian as an example, this paper analyzes the interaction of the excavation steps and the change rule of the 3D stress field and strain field in the tunnel by establishing a 3D excavation numerical model with 3D -Sigma software, using the measured stress data as a boundary condition and determining the inputs of the rock mass with the Hoek -Brown strength criterion. The results show that: because of high ground stress, compressive stress concentration occurs at the tunnel crown and shear stress concentration occurs at the spandrel, which may cause brittle failure at the tunnel wall; previously excavated tunnel sections may be affected by subsequent excavation, making the stress concentration effect more obvious and the failure of the surrounding rock more serious; the actual rockburst locations correspond with the locations of maximum compressive stress concentration and maximum shear stress concentration in simulation analysis. The numerical simulation can clearly reveal the mechanism and the possible law of the rock burst, providing strong technical support for engineering applications.

Xu J.S.,Chinese Institute of Crustal Dynamics
Applied Mechanics and Materials | Year: 2014

Determining the in-situ stress of wall rock is important for the underground cavern project. The three-dimensional (3-D) stress measurement, which is obtained by hydraulic fracturing stress measurement via measuring the stresses in boreholes with three different orientations, has been applied for the designation of cavern project. However, there are few examples that can demonstrate the reliability of 3-D stress measurement method. In this study, we showed one example of the 3-D stress results measured by hydraulic fracturing in Western China. The measured results, especially the dip angles of the maximum principle stress are consistent with those determined by focal mechanism of nearby earthquakes. This consistence indicates the reliability of the 3-D stress results by hydraulic fracturing and an expected application for regional geostress study. © (2014) Trans Tech Publications, Switzerland.

Zhu X.,Chinese Institute of Crustal Dynamics
Earthquake | Year: 2015

Earth resistivity observation is from the DC power supply to more powerful pulse power supply with sinusoidal AC power supply, but the earth capacitive effects will cause observation error. This paper analyzes the effects of earth capacitance from the supply perspective. According to the method of equivalent circuit electronics, I put forward the concept of the equivalent capacitance of the earth. The relationship between equivalent capacitance of the earth and frequency and polar distance has been found based on experiment observations. ©, 2015, Science Press. All right reserved.

Zhang G.-W.,Chinese Institute of Crustal Dynamics | Lei J.-S.,Chinese Institute of Crustal Dynamics | Liang S.-S.,China Earthquake Networks Center | Sun C.-Q.,Chinese Institute of Crustal Dynamics
Chinese Journal of Geophysics (Acta Geophysica Sinica) | Year: 2014

Using the double-difference algorithm, we relocated the Ludian MS6.5 mainshock and its 647 aftershocks during 3 to 7 August 2014 and finally obtained 471 relocated earthquakes. Our results show that the focal depth of main shock is 13.3 km, which is close to the initial rupture depth of the main shock. The aftershock sequence presents an asymmetric conjugate shape with lengths of 17 km in the EW direction and of 22 km in the NW direction. Small earthquakes are predominately located above 10 km depth, and extend toward the shallow parts above 10 km depth along the southeast and eastwest directions of conjugate faults from the main shock. In addition, distribution of small earthquakes also shows that the seismogenic fault has a high dip and is the NW Baogunao-Xiaohe fault that is one branch of the Zhaotong-Ludian fault. Because the mainshock centroid depth can provide important evidence for understanding the serious disaster caused by the mainshock, we determined 5 focal mechanism solutions (MS≥4.0) including the main shock using the gCAP(generalized Cut And Paste) method. Our results show that the centroid depth of the main shock is only 5 km, which is consistent with the 2~8 km depth of larger slip in the obtained rupturing process. The conjugate rupture and shallower centroid depth of main shock could be the important causes for the serious disaster of this earthquake.

Zhou Z.,Chinese Institute of Crustal Dynamics | Lei J.,Chinese Institute of Crustal Dynamics
Physics of the Earth and Planetary Interiors | Year: 2016

We present a new high-resolution Pn anisotropic tomographic model of the uppermost mantle beneath China inferred from 52,061 Pn arrival-time data manually picked from seismograms recorded at provincial seismic stations in China and temporary stations in Tibet and the Tienshan orogenic belt. Significant features well correlated with surface geology are revealed and provide new insights into the deep dynamics beneath China. Prominent high Pn velocities are visible under the stable cratonic blocks (e.g., the Tarim, Junngar, and Sichuan basins, and the Ordos block), whereas remarkable low Pn velocities are observed in the tectonically active areas (e.g., Pamir, the Tienshan orogenic belt, central Tibet and the Qilian fold belt). A distinct N-S trending low Pn velocity zone around 86°E is revealed under the rift running from the Himalayan block through the Lhasa block to the Qiangtang block, which indicates the hot material upwelling due to the breaking-off of the subducting Indian slab. Two N-S trending low Pn velocity belts with an approximate N-S Pn fast direction along the faults around the Chuan-Dian diamond block suggest that these faults may serve as channels of mantle flow from Tibet. The fast Pn direction changes from N-S in the north across 27°N to E-W in the south, which may reflect different types of mantle deformation. The anisotropy in the south could be caused by the asthenospheric flow resulted from the eastward subduction of the Indian plate down to the mantle transition zone beneath the Burma arc. Across the Talas-Fergana fault in the Tienshan orogenic belt, an obvious difference in velocity and anisotropy is revealed. To the west, high Pn velocities and an arc-shaped fast Pn direction are observed, implying the Indo-Asian collision, whereas to the east low Pn velocities and a range-parallel Pn fast direction are imaged, reflecting the northward underthrusting of the Tarim lithosphere and the southward underthrusting of the Kazakh lithosphere. In most parts of eastern China, pronounced low Pn velocities and a complex anisotropy pattern are observed, implying the re-orientation of the olivine arrangement in the thin lithosphere due to the westward subduction of the Pacific plate. © 2016 Elsevier B.V.

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