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881.
882.
883.
数字水准仪的出现解决了大地测量仪器中水准仪自动读数与记录问题,对当代测量技术产生了积极的影响。文中介绍了如何采用双频激光干涉仪配合45°平面镜检测数字水准仪的方法,对精密光学水准仪和数字水准仪进行综合精度的评定和比较,并对结果进行了分析。 相似文献
884.
介绍了航空激光扫描(Airborne laser scanning)或者Lidar遥感信息获取系统的基本原理、系统的组成、数据获取的方法及其步骤;对近数十年来应用激光扫描遥感信息获取地形表面模型方面取得的主要成果、应用现状做了简要回顾和评述;结合GIS和影像融合方法对Lidar遥感技术未来发展趋势进行了展望。 相似文献
885.
886.
887.
本文在利用多台研究1999年11月29日和2000年1月12日发生在辽宁岫岩Ms5.4级和5.1级地震前拐角频率比随时间变化的基础上,对岫岩、营口、苏家屯、丹东、宽甸、北镇、新民单台记录的纵横波拐角频率比fcp/fcs做了比较详细的波谱分析。结果表明:在震中距小于200 km以内的不同方向的台站,记录到的地震波拐角频率比值在5.4级前和后均出现不同程度的异常显示,能够捕捉到一些带有短临性质的信息,不过,距震中较远的台站,地震波拐角频率比值在震前异常不如近台明显,表明不同距离的台站,记录的地震拐角频率比值存在着差异。 相似文献
888.
The structural activities took place extensively in the Asia continent during the Cenozoic era owing to the strong continent-to-continent
collision and continuous compression between the India Plate and the Eurasia Plate. Huang Jiqing called such structural activities
Himalayan movement. China’s sedimentary basins developed and took shape mainly during the Himalayan movement period. It is
also the main period for formation and development of the oil and gas reservoirs. Of 366 large and medium-sized oil and gas
fields currently found in China, 212 reservoirs were formed in the Neogene-Quaternary period. The proportion is as high as
68.2%. The oil and gas migration and accumulation in the latest geological period, which were controlled by the times, properties,
styles and strength of the Himalayan movement, took place mainly in eight regions, such as the low uplift area of Bohai Sea,
the onshore faulted sag area of Bohai Bay, anticlinorium zone in Daqing, the foreland fold-and-thrust belt in West China,
the tilted structural zone in West China, the cratonic palaeohigh in the Tarim Basin, the zone of fault and fold belt in the
East Sichuan Basin, and the biological gas zone in the East Qaidam Basin. The oil and gas pool formations in those regions
have their own characteristics. With the great potential and broad prospect, those regions are the main exploration areas
in China in the future. 相似文献
889.
Arthur Rodgers Hrvoje Tkalcic David McCallen Shawn Larsen Catherine Snelson 《Pure and Applied Geophysics》2006,163(1):55-80
We report site response in Las Vegas Valley (LVV) from historical recordings of Nevada Test Site (NTS) nuclear explosions
and earthquake recordings from permanent and temporary seismic stations. Our data set significantly improves the spatial coverage
of LVV over previous studies, especially in the northern, deeper parts of the basin. Site response at stations in LVV was
measured for frequencies in the range 0.2–5.0 Hz using Standard Spectral Ratios (SSR) and Horizontal-Vertical Spectral Ratios
(HVR). For the SSR measurements we used a reference site (approximately NEHRP B ``rock' classification) located on Frenchman
Mountain outside the basin. Site response at sedimentary sites is variable in LVV with average amplifications approaching
a factor of 10 at some frequencies. We observed peaks in the site response curves at frequencies clustered near 0.6, 1.2 and
2.0 Hz, with some sites showing additional lower amplitude peaks at higher frequencies. The spatial pattern of site response
is strongly correlated with the reported depth to basement for frequencies between 0.2 and 3.0 Hz, although the frequency
of peak amplification does not show a similar correlation. For a few sites where we have geotechnical shear velocities, the
amplification shows a correlation with the average upper 30-meter shear velocities, V30. We performed two-dimensional finite difference simulations and reproduced the observed peak site amplifications at 0.6 and
1.2 Hz with a low velocity near-surface layer with shear velocities 600–750 m/s and a thickness of 100–200 m. These modeling
results indicate that the amplitude and frequencies of site response peaks in LVV are strongly controlled by shallow velocity
structure. 相似文献
890.
Threat level green: Conceding ecology for security in eastern Europe and the former Soviet Union 总被引:1,自引:0,他引:1
Following the collapse of the Soviet Union, the predicted scenarios of Central Asian water wars and catastrophic nuclear accidents have failed to materialize. However, the Aral Sea continues to shrink apace, and dangerous Soviet-built nuclear reactors have since proliferated in the former eastern bloc. These seemingly paradoxical outcomes can in part be attributed to the framing of these environmental issues as security matters by leading international regulatory, aid and lending institutions. Integrating these environmental concerns with the realist worldview of security studies systematically emphasized security dimensions at the expense of ecological concerns even amongst organizations distant from traditional defense affairs. This article proposes that international security strategy in this period is one of environmental appeasement defined as the systematic granting of ecologically unfriendly concessions in order to reduce short-term security risks. The article presents evidence that this appeasement strategy generated seemingly impressive results in terms of ameliorating short-term security risks, while actually exacerbating the underlying ecological situation. The article argues that while the foundational environmental risks remain unaddressed, the associated security threats have likewise not been ultimately resolved. 相似文献