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991.
Anisotropic reverse-time migration for tilted TI media 总被引:1,自引:0,他引:1
Seismic anisotropy in dipping shales results in imaging and positioning problems for underlying structures. We develop an anisotropic reverse‐time depth migration approach for P‐wave and SV‐wave seismic data in transversely isotropic (TI) media with a tilted axis of symmetry normal to bedding. Based on an accurate phase velocity formula and dispersion relationships for weak anisotropy, we derive the wave equation for P‐wave and SV‐wave propagation in tilted transversely isotropic (TTI) media. The accuracy of the P‐wave equation and the SV‐wave equation is analyzed and compared with other acoustic wave equations for TTI media. Using this analysis and the pseudo‐spectral method, we apply reverse‐time migration to numerical and physical‐model data. According to the comparison between the isotropic and anisotropic migration results, the anisotropic reverse‐time depth migration offers significant improvements in positioning and reflector continuity over those obtained using isotropic algorithms. 相似文献
992.
993.
J. Du W.E. Ward J. Oberheide T. Nakamura T. Tsuda 《Journal of Atmospheric and Solar》2007,69(17-18):2159
The extended Canadian Middle Atmosphere Model (extended CMAM) is a general circulation model, which extends from the surface to about 210 km. Spatial complex spectral analysis is applied to horizontal winds simulated by the extended CMAM to obtain semidiurnal tidal amplitudes and phases (from e5 to w5) in the mesosphere and lower thermosphere (MLT) region. The dominant w2 migrating component and the presence of eight nonmigrating tides (w3, w4, w5, e1, e2, e3, e4 and e5) in the mid-latitudes are identified. Components w1 and s0, which tend to maximize at high latitudes, will be discussed separately in a later paper. The migrating semidiurnal tide (w2) has amplitudes reaching over 20 m s−1 for both zonal and meridional winds in the mid-latitude region. Its form compares well to the published results. The amplitudes of nonmigrating semidiurnal tides are non-negligible compared with the migrating semidiurnal tides. The amplitudes for w3 and e2 exceed 12 and 8 m s−1, respectively.Comparisons are made with four nonmigrating semidiurnal components (w3, w4, e1 and e2) derived from the TIMED Doppler interferometer (TIDI) wind measurements between 85 and 105 km altitude and between 45°S and 45°N latitude. Overall, the basic CMAM and TIDI latitudinal structures of the amplitudes agree well and the agreement between the annual mean amplitudes varies with component. Relative to the TIDI results, the CMAM seasonal variations of w4 are in good agreement, of e2 are in reasonable agreement, of w3 are in partial agreement and of e1 are in poor agreement.The 11 semidiurnal components from the model are superimposed to generate the total semidiurnal winds at Jakarta (6°S, 106°E) and Kototabang (0°, 100°E) and are compared with measurements from two equatorial meteor radar stations at these sites. The relative contributions of components to the reconstructed amplitude vary from month to month. The CMAM reconstructions are generally larger than the radar results by a factor varying between one and two. The phases in the radar data are typically stationary with respect to height, whereas they generally decrease with height in the CMAM reconstruction. 相似文献
994.
995.
Nonlinear seismic response analysis of arch dam-foundation systems- part I dam-foundation rock interaction 总被引:1,自引:0,他引:1
The arch dam–foundation rock dynamic interaction and the nonlinear opening and closing effects of contact joints on arch dam
are important to the seismic response analysis of arch dams. Up to date, there is not yet a reasonable and rigorous procedure
including the two factors in seismic response analysis. The methods for the analysis of arch dam–foundation rock dynamic interaction
in frequency domain are not suitable to the problem with nonlinear behaviors, in this paper, so an analysis method in time
domain is proposed by combining the explicit finite element method and the transmitting boundary, and the dynamic relaxation
technique is adopted to obtain the initial static response for dynamic analysis. Moreover, the influence of arch dam–foundation
dynamic interaction with energy dispersion on seismic response of designed Xiaowan arch dam in China is studied by comparing
the results of the proposed method and the conventional method with the massless foundation, and the local material nonlinear
and nonhomogeneous behaviors of foundation rock are also considered. The reservoir water effect is assumed as Westergaard
added mass model in calculation. The influence of the closing–opening effects of contact joints of arch dam on the seismic
response will be studied in another paper. 相似文献
996.
997.
Land cover changes based on plant successions: Deforestation,rehabilitation and degeneration of forest in the upper Dadu River watershed 总被引:2,自引:0,他引:2
Jianzhong?Yan Yili?ZhangEmail author Wanqi?Bai Yanhua?Liu Weikai?Bao Linshan?Liu Du?Zheng 《中国科学D辑(英文版)》2005,48(12):2214-2230
The land use/cover classification system is the foundation for land use/cover change study. Remote sensing data were firstly used for land use and land cover classification in the United States in 1971 and the Anderson Classification System was proposed in 1976[1], which was put into use in mapping 1:250000 land use and land cover of the United States. A series of new land cover classification systems have been established in recent years through research projects such as FAO LCCS and Bi… 相似文献
998.
Dušan Němec 《Mineralogy and Petrology》1964,9(1-2):42-85
Ohne ZusammenfassungMit 18 Textabbildungen 相似文献
999.
The Baishan Mo–Re deposit is located in the eastern section of the eastern Tianshan orogenic belt, NW China. The deposit has a grade of 0.06% Mo and a high content of rhenium of 1.4 g/t. Rhenium and osmium isotopes in sulfide minerals from the Baishan deposit are used to determine the age of mineralization. Rhenium concentrations in molybdenite samples are between 74 and 250 g/g. Analysis of eight molybdenite samples yields an isochron age of 224.8±4.5 Ma (2). Pyrite samples have rhenium and osmium concentrations varying in the range 33.4–330.6 ng/g and 0.08–0.81 ng/g, respectively. Isotope data on seven pyrite samples yield an isochron age of 225±12 Ma (2) on the 187Re/188Os versus 187Os/188Os plot and an age of 233±14 Ma (2) on the 187Os versus 187Re correlation diagram. The ages of molybdenite and pyrite are consistent within the analytical errors. Combined with field observations, the data indicate that Mo–Re mineralization in the Baishan deposit is produced by a magmatic-hydrothermal event in an intracontinental extensional setting after late Paleozoic orogeny. The initial 187Os/188Os ratio of pyrite is 0.3±0.07. The 34S values of molybdenite vary from +0.5 to +3.6. Both data indicate that mineralization is derived mainly from a mantle source.Editorial handling: J. Richards 相似文献
1000.
地震趋势预测的一种新模型研究 总被引:5,自引:0,他引:5
本文根据自激励门限自回归模型原理,对多年的地震活动形势进行了分析,建立了用于地震大形势分析的客观化数值预测模式-在线预测模型。根据1980年以来中国大陆实际发生的地震资料对这一模型的可靠性进行了检验。统计结果表明,利用在线预测模型在对未来地震趋势进行预测时,其年度形势特征量的最大误差为0.3,平均误差为0.12;因此该模型能够比较客观地反映地震形势变化的自然特征及规律,较好的预测未来的地震活动趋势。这一模型的建立为促进地震趋势向客观化、定量化预测方向发展,提供了一种科学途径 相似文献