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101.
本文讨论利用三维反射地震数据进行波场反演的一种方法,旨在取得高分辨率的地球模型.这种方法用Backus-Gilbert的理论构造波动方程非线性反问题的逐次线性化迭代格式,用逆散射原理导出泛函的Frechet导数,并用最佳折衷准则求解线性化后的方程组.根据迭代过程中不断提高分辨率的思想和减少计算成本的原则,设计了可供实用的反演算法流程. 相似文献
102.
The analysis and interpretation of coda waves have received increasing attention since the early seventies. In the past few years interest in this subject has spread worldwide, and the study of high-frequency seismic coda waves has become a very important seismological topic. As a conclusion of the studies accomplished in this time, coda waves are considered the result of scattering processes caused by heterogeneities acting on seismic waves.P andS waves play a particularly important role in this interaction. The process introduces an attenuation which, added to the intrinsic absorption, gives the observed apparent attenuation. Therefore, coda waves constitute a thumbprint left by the heterogeneities on the seismograms. Coda waves offer decisive information about the mechanism of how scattering and attenuation take place. This review describes coda waves in detail, and summarizes the work done in this subject to 1986. The relation between coda waves and attenuation in the context of research on seismic scattering problems is stressed. Particular attention has been given to the application of coda waves to estimate source and medium parameters. The state-of-the-art of the temporal variations of coda wave shape, and the possible use of these variations as an earthquake precursor also are presented. Care has been taken to introduce the statistical models used to deal with the heterogeneities responsible for scattering. 相似文献
103.
The formal solutions of displacement field to the problem of elastic wave scattering and diffraction due to an infinitely long rigid cylinder embedded in an infinite elastic medium by an impulsive point source have been obtained in the integral form. The integrals for the reflected and the diffracted waves both in the shadow zone and in the illuminated zone are evaluated asymptotically for the early time motion by the Reisdue-Cagniard method and the Saddle-point-Cagniard method.Numerical results of the diffractedP, S andPS waves at a fixed circum-distance from the surface of the rigid cylinder show noticeably that (1) the energy partition for the diffractedS wave is small in comparison with that for the diffractedP wave, (2) the wave form of the diffractedS wave is broader and more diffused than that of the diffractedP wave, (3) the direction of the radial motions of the diffractedP andS waves varies as a function of the observational point, and (4) the energy partition for the diffractedP wave is much smaller than that for the direct or the reflectedP waves.This paper has been presented at the 46th Annual International Meeting of Society of Exploration Geophysicists in Houston, Texas, Oct. 28, 1976. 相似文献
104.
C. O. Oluwafemi 《Pure and Applied Geophysics》1983,121(5-6):1065-1076
Solar, sky, and aureole radiance data from Kensington, Australia, and Lagos, Nigeria, are analysed. The values of the aerosol
optical thickness at Lagos are comparable to measured values elsewhere in the subregion (Abidjan) under light haze. The values
at Kensington are close to those of the “background aerosol.” Identical and anomalous values of aerosol optical thickness
occurred at 1.67 μm at both stations as less than 15% of the values can be accounted for by aerosols. The high optical depths
are therefore explained in terms of absorption, possibly mainly by CO2 (59–65%) and, to a lesser extent, by H2O (20–26%). Following correction for molecular multiple scattering, the aerosol scattering phase function increases substantially
at 0.5 μm in Kensington and decreases considerably at 0.76 μm in Lagos when compared to the uncorrected function, confirming
the relative fineness of the Kensington aerosol. The Lagos aerosol size distribution for moderately dusty air is reasonably
bimodally log-normal with modal radiusr
m=0.49 μm (1.36 μm) for the moder≤1 μm (r>1 μm). The Kensington aerosol resembles one withr
m=0.05 μm forr<1 μm. There the Born approximation appears appropriate, and the weighted mean square radiusp
2=0.13 μm2. In the near forward direction the aerosol scattering phase funciton for Lagos resembles Deirmendjian’s simulations for a
silicate-L haze and, for Kensington, a silicate-H haze. 相似文献
105.
106.
结合安徽省高速公路建设工程实例,介绍瞬态瑞雷面波勘探技术在公路工程地质勘察中的应用,解决沿线高边坡、深路堑、桥梁、隧道进出口的岩土分层,给出基岩风化分带等工程地质问题,省时、省力,取得了良好的经济效益和环境效益. 相似文献
107.
Limitations of real-time models for forecasting river flooding from monsoon rainfall 总被引:1,自引:0,他引:1
Very intense rainfall during the southwest and northeast monsoons causes severe river flooding in India. Some traditional
techniques used for real-time forecasting of flooding involve the relationship between effective rainfall and direct surface
runoff, which simplifies the complex interactions between rainfall and runoff processes. There are, however, serious problems
in deducing these variables in real time, so it is highly desirable to have a real-time flood forecasting model that would
directly relate the observed discharge hydrograph to the observed rainfall. The storage routing model described by Baba and
Hoshi (1997), Tanaka et al. (1997), and Baba et al. (2000), and a simplified version of this model, have been used to compute observed river discharge directly from observed hourly
rainfall. This method has been used to study rainfall–runoff data of the Ajay River Basin in eastern India. Five intense rainfall
events of this basin were studied. Our results showed that the Nash–Sutcliffe efficiency of discharge prediction for these
five events was 98.6%, 94.3%, 86.9%, 85.6%, and 67%. The hindcast for the first two events is regarded as completely satisfactory
whereas for the next two events it is deemed reasonable and for the fifth it is unsatisfactory. It seems the models will yield
accurate hindcast if the rainfall is uniform over the drainage basin. When the rainfall is not uniform the performance of
the model is unsatisfactory. In future this problem can, in principle, be corrected by using a weighted amount if rainfall
is based upon multiple rain-gauge observations over the drainage basin. This would provide some measure of the dispersion
in the rainfall. The model also seems unable to simulate flooding events with multiple peaks. 相似文献
108.
Three cores from two connected lakes in Central Ireland (Lough Kinale and Derragh Lough) were investigated using diatom analysis
to establish the Holocene development of the lacustrine system, any local variations within the lakes and any anthropogenic
influences. The study area was situated in a lowland location and the lakes were shallow, unstratified and interconnected.
Litho-and bio-stratigraphical analyses of the lake cores and deposits beneath a mire separating the two lakes showed the changing
spatial configuration of the lake system in the early Holocene and the separation of the initial lake into three basins (cf.
lacustrine cells) and finally into two interlinked lakes. The evolution of the lake system is conceptualised as the development
of distinct lacustrine cells, and its sediments have recorded changes in the physical (geography, depth and sedimentation)
and chemical (water chemistry) properties of the lakes inferred through diatom analyses. The longest sequence, from the early
Holocene, records fluctuating lake levels and these are correlated with geomorphological mapping and surveying of palaeoshorelines.
The diatom assemblages of the upper 2 m of the three cores, covering approximately the last 2000–3000 radiocarbon years show
considerable difference in trophic status and life-form categories. This is related to the location of the cores in the lake
and also the distance from human settlement with particular reference to proximity to crannog (artificial island) construction
and use. The most central core from the deepest part of Lough Kinale has the least representation of the human settlement
and agricultural activity in the catchment and on the fringes of the lake, whereas the core taken from the edge of a crannog
is able to identify when construction and use of the crannog occurred. The local nature of the palaeoecological response to
human activity due to incomplete water mixing has the advantage of allowing the lake sediment cores to be used to determine
spatially discrete settlement patterns. 相似文献
109.
110.
利用Fourier Bessel级数展开法,给出了表面具有覆盖层的圆弧形凹陷地形对入射平面SV波散射问题的一个解析解,并利用该解分析了不同深宽比凹陷地形表面覆盖层刚度和厚度对入射SV波的影响.结果表明,凹陷地形表面覆盖层的存在,即使厚度很薄,也会显著增加对入射SV波的放大作用,该放大作用可达到单一凹陷地形的2.5倍以上.覆盖层刚度和厚度的变化对入射平面SV波也具有很大影响. 相似文献