Seismic migration and absorbing boundaries with a one-way wave system for heterogeneous media1     

Nanxun Dai  Antonios Vafidis  Ernest R. Kanasewich 《Geophysical Prospecting》1996,44(4):719-739

A first-order one-way wave system has been created based on characteristic analysis of the acoustic wave system and optimization of the dispersion relation. We demonstrate that this system is equivalent to a third-order scalar partial-differential equation which, for a homogeneous medium, reduces to a form similar to the 45° paraxial wave equation. This system describes accurately waves propagating in a 2D heterogeneous medium at angles up to 75°. The one-way wave system representing downgoing waves is used for a modified reverse time migration method. As a wavefield extrapolator in migration, the downgoing wave system propagates the reflection events backwards to their reflectors without scattering at the discontinuities in the velocity model. Hence, images with amplitudes proportional to reflectivity can be obtained from this migration technique. We present examples of the application of the new migration method to synthetic seismic data where P-P reflections P-SV converted waves are present. Absorbing boundaries, useful in the generation of synthetic seismograms, have been constructed by using the one-way wave system. These boundaries absorb effectively waves impinging over a wide range of angles of incidence.  相似文献   

On the seismic regime network method     

Zegao Wang  Yan Guo  Shulian Li  Yinghua Dai  Peiqing Sun 《地震学报(英文版)》1992,5(2):245-255

In this paper, based on the previous study of practical use of seismic regime windows and seismic regime belts, the problem of establishing a “seismic regime network” consisting of “windows” and “belts” is further posed and discussed according to the observed fact that many “windows” and “belts” make responses to one earthquake. For the convenience of usage, the “seismic regime network” is divided into two classes, the first class and the second one. The former can be used in tendency prediction for long-term seismic activity in a large area, the latter used in short-term prediction in a small area. In this paper, after briefly discussing the physical significance of “seismic regime network”, it is pointed out that this simple and easily used method can be used to observe and extract seismic precursory information from a large area before a great earthquake, thus it can provide a reliable basis for the analysis and judgement of seismic regime tendency in time and space. No doult, this method is of certain practical significance. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 161–169, 1991. The English version of this paper is improved by Prof. Shaoxie Xu.  相似文献   

贺兰山群变质杂岩主期变质作用的温压环境研究   总被引：1，自引：0，他引：1  

杨家喜  胡能高 《矿物岩石》1992,12(4):12-20

分布于贺兰山脉北部的贺兰山群变质杂岩的主期变质作用达角闪麻粒岩相,其矿物组合特征与低压相系麻粒岩相似、利用共生矿物组合和矿物对的温度计、压力计估算主期变质温度740—764(?),压力460—501MPa。温度压力条件与低压相系的地热梯度线较接近,变质作用强度具面型分布的特征,与东部密云、冀东等地的麻粒岩相区相似,但变质压力明显低,压力类型也不同,应属不同构造背景下的变质产物。  相似文献   

康滇地轴中,新元古代不整合面铀矿远景分析     

戴杰敏 《铀矿地质》1992,8(6):329-337

  相似文献   

四川省青川断裂的特征及形成的物理条件   总被引：3，自引：0，他引：3  

代建全 《四川地质学报》1992,(4)

本文详细地讨论了四川省青川断裂的断裂特征及形成的物理条件。对断裂构造岩的微构造和宏观构造进行了细致的描述分析,将断裂岩分为四个带。结合区域资料,讨论了断裂的形成时代及与邻区的关系。  相似文献   

机车车辆滚动振动试验台的精密测量     

岑敏仪  唐恩利 《四川测绘》1995,18(1):34-38

本文针对国家重点牵引力动力实验室的机车车辆整车滚动振动试验台的特点，探讨了一套适合试验台安装和养护的精密测量方法，实践证明，这套方法能满足试验台安装所需的精度要求。  相似文献   

用CAPPI和PPI资料测定区域降水量精度比较   总被引：5，自引：0，他引：5  

戴铁丕  詹煌  刘婉莉 《气象》1995,21(7):9-14

应用上海中心气象台７１４数字化天气雷达的体积扫描资料所得的不同高度上的ＣＡＰＰＩ资料和低仰角时ＰＰＩ资料。估算区域降水量并得到降水量分布形势。然后采用平均校准法进行了校准，最后又与用雨量计网测量的区域降水量及其分布形势作了比较，得到一些有意义的结果。  相似文献   

Reducing global warming — The role of rice     

Heinz-Ulrich Neue  Lewis H. Ziska  Robin B. Matthews  Qiujie Dai 《GeoJournal》1995,35(3):351-362

Activities to provide energy for an expanding population are increasingly disrupting and changing the concentration of atmospheric gases that increase global temperature. Increased CO₂ and temperature have a clear effect on growth and production of rice as they are key factors in photosynthesis. Rice yields could be increased with increased levels of CO₂, however, the rise of CO₂ may be accompanied by an increase in global temperature. The effect of doubling CO₂ levels on rice production was predicted using rice crop models. They showed different effects of climate change in different countries. A simulation of the Southeast Asian region indicated that a doubling of CO₂ increases yield, whereas an increase in temperature decreases yield.Enhanced UV-B radiation resulting for stratographic ozone depletion has been demonstrated to significantly reduce plant height, leaf area and dry weight of two rice cultivars under glasshouse conditions. Data are still insufficient, however, for conclusive results on the effect of UV-B radiation on rice growth under field conditions.Rice production itself has a significant effect on global warming and atmospheric chemistry through methane emission from flooded ricefields. Water regime, soil properties and the rice plant are major factors controlling the flux of methane in ricefields. Global and regional estimates of methane emission rates are still highly uncertain and tentative. Integration of mechanistic modeling of methane fluxes with geographic information systems of factors controlling these processes are required to improve estimates and predictions.  相似文献   

大型抽水试验最优化设计研究     

戴振学 《吉林大学学报(地球科学版)》1993,(1)

抽水试验最优化设计,是指针对一个具体的地下水系统优选出一个抽水试验设计,它使抽水试验的费用最小化,而试验所获资料能满足识别参数所要求的可靠性,它可以概化为一个非线性的混合整数规划问题,其决策变量是确定抽水井和观测井的位置及井数、抽水量和观测频率等,采用搜索算法求解了这一优化问题,得到了理论最优解,并进行了实例演算。  相似文献   

皖南地区谭山复式岩体的成因研究          下载免费PDF全文

陈秀其周涛发  戴圣潜张达玉徐锦龙  汪雅菲吴 衡 吴 昊 葛海影 《地质科学》1958,55(4):1152-1178

谭山复式岩体位于江南过渡带北缘,是该区出露面积较大的复式岩体。本文对谭山复式岩体开展了地质调查、岩浆岩锆石U-Pb年代学和全岩地球化学分析。地质特征显示谭山复式岩体沿杨美桥背斜轴部侵入,根据岩性分析划分为碱长花岗岩、正长花岗岩和二长花岗岩。LA-ICP-MS锆石U-Pb定年结果显示,碱长花岗岩和正长花岗岩分别为128.9±1.6 Ma～128.8±2.5 Ma和129.8±2.6 Ma～129.2±1.8 Ma;结合前人已获得二长花岗岩成岩时代（128.5±1.7 Ma～126.7±1.7 Ma）,谭山复式岩体形成于128.9±1.6 Ma～126.7±1.7 Ma之间,对应于皖南地区燕山期 3阶段岩浆活动（早阶段：153～146 Ma,中阶段：143～136 Ma,晚阶段：135～121 Ma）的最晚阶段（135～121 Ma）。该复式岩体碱长花岗岩、正长花岗岩和二长花岗岩的地球化学特征均表现为：富碱,高Ga/Al比值,强烈亏损Ba、Sr、P、Ti,富集 Rb、Th、Nd、Ce,显著的Eu负异常,均为碱性过铝质特征的A型花岗岩。谭山复式岩体起源于下地壳物质部分熔融,为陆内拉张环境背景下同源岩浆多期次上升侵位的产物。  相似文献