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661.
Seismic tomography is one of the main tools to explore the interior of the earth.In this study,the quasi-waveform seismic tomographic method is used for the first time to reveal the crustal structures in the capital region of China.3-D highresolution V_P,V_S and the Poisson’s ratio models are generated by inverting 29839 direct P-and 29972 direct S-wave traveltimes selected from 3231 local earthquakes.The results reveal strong crustal heterogeneities.The velocity anomalies at shallow depths are well consistent with surface geologic structures.The relatively low-velocity anomaly layer in the middle crust may be the result of multiple phases of tectonic activity.Earthquakes generally occurred on the boundaries of high-and low-velocity and Poisson’s ratio anomalies.There are obvious low-velocity anomalies below the hypocenters of the Tangshan earthquake and the historical Sanhe-Pinggu earthquake,implying the existence of fluids.The similar velocity structures around the hypocenters of the two earthquakes indicate that the occurrences of the two earthquakes may be related to the same mechanism.The highresolution velocity models provide important observational constraints on the small-scale heterogeneities and dynamic mechanism of the crust in the capital region of China. 相似文献
662.
Shaking table tests were conducted on saturated clean Vietnam sand in the large biaxial laminar shear box (1880 mm×1880 mm×1520 mm) at the National Center for Research on Earthquake Engineering (NCREE), Taiwan. The settlement of sand specimens was measured and evaluated during and after each shaking test. Without liquefaction, the settlement of sand caused by shaking is very small. Significant volume changes occur only when there is liquefaction of sand. The volumetric strain of liquefied sand was calculated according to the measured settlement and the thickness of liquefied sand in the specimen. Relations between volumetric strain after liquefaction and the relative density of saturated clean sand were developed for various shaking durations and earthquake magnitudes. They are not affected by the shaking amplitude, frequency, and direction (one- or multidirectional shaking). 相似文献
663.
Intergranular coesite and coesite inclusions in dolomite from the Dabie Shan: Constraints on the preservation of coesite in UHP rocks 下载免费PDF全文
Intergranular coesite is extremely rare in, and bears crucial information on the formation and preservation of, ultrahigh‐pressure (UHP) rocks. Here, we report the first occurrence of intergranular coesite in a metasedimentary rock, which occurs in the Ganjialing area in the Dabie Shan, east‐central China, and contains abundant coesite inclusions in both garnet and dolomite. We investigated the content of structural water in these minerals with Fourier transform infrared spectroscopy. Our new results undermine the ubiquity of the “pressure‐vessel” model and highlight the role of reaction kinetics in preserving coesite due to the availability of water in UHP rocks. 相似文献
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The axisymmetric finite element technique is used in this paper to analyze the creep effects on pole foundation. Generalized Kelvin model and Bingham model are proposed to simulate the viscoelastic and viscoelastic behavior of soil respectively. Viscoelastic and viscoelastic strain incremental formulas are derived for interface elements and soil elements around piles and the axisymmetric elastic-viscoelastc-viscoplastic finite element program is compiled. Creep effects on the settlement of poles, the building load carried by raft and the distribution of stresses along piles are analyzed. In addition, the behavior of interface between pile and soil are investigated through experiment. 相似文献
668.
Orogenic and Anorogenic Granitoids in the Altay Mountains of Xinjiang and Their Discrimination Criteria 总被引:1,自引:0,他引:1
On the basis of field geological studies of the granotoids in the region, mineralogical, petrological, geochemical(including stable isotope geochemical) and isotopic geochronological investigations were carried out on selected representative granitic bodies of various types. The authors have concluded that, apart from the bodies of the orogenic granitoid series, there also exist intrusions of the anorogenic granitoid series in the region. The intrusives of the two series were formed not only in different ages and tectonic environments, but also were derived from different sources of materials. Moreover, they are associated with different mineralizations, belonging to different minerologenetic series(Cheng et al., 1983). They show distinctly a series of discriminative criteria. The problems under discussion in the present paper are of important theoretical and practical significance in the studies of granites of the orogenic belt, particularly the studies of the genesis and related metallogeny of the granites of the region. 相似文献
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Wu Zhishan Lin Junqin 《吉林大学学报(地球科学版)》1989,(4)
本文用加权剩余法导出点源二维地电断面的边界单元法积分方程。通过付氏反变换,可获得三维空间的电位。若干模型上正演计算结果与解析解完全一致。对实测的ρ_s曲线进行了地形攻正及选择法反演拟合,解释结果与实际地质断面符合得很好。 相似文献