But was there one major wave of migration across the Bering Strait into the Americas, or several?
但是有没有一次或几次大移民浪潮是穿过白令海峡到达美洲的呢？
The third wave, perhaps 10,000 or 9,000 years ago, saw the migration from North-east Asia of groups ancestral to the modern Eskimo and Aleut.
第三次浪潮大约发生在一万或九千年前，见证了东北亚的祖先群体向现代爱斯基摩人和阿留申人的迁移。
"Old America seemed to be breaking up and moving westward," observed an English visitor in 1817, during the first great wave of migration.
1817年，在第一次移民大潮中，一位英国游客观察到：“古老的美洲似乎正在分裂并向西移动。”
Wave equation time migration fails to image subsurface geological structure correctly in the case of obvious lateral seismic velocity variation.
当介质的速度在横向上存在较大的变化时，波动方程时间偏移不能使地下的构造正确成像。
Wave equation prestack depth migration technique is an effective method of seismic data imaginating in complicated surfaces.
波动方程叠前深度偏移技术是复杂地表地震资料成像的有效方法。
The era of globalization saw the largest wave of human migration in history.
全球化时代经历了历史上最大了人口迁移浪潮。
The application of such one-way wave equation to exploiting WIMIG module for migration is described finally.
最后给出了构造的单程波动方程在开发常规WIMIG偏移模块中的应用。
The purpose of migration is to inversely solve for the singularity (interrupted surface of interval velocity) of wave equation coefficient.
偏移的目的是要反演波动方程系数的奇性(层速度的间断面)。
As the most physical of the shot-profile wave equation pre-stack depth migration involving huge extrapolation calculation, the calculation is extremely time-consuming and less efficient.
作为最具物理性的共炮点道集的波动方程叠前深度偏移，涉及庞大的波场外推计算量，计算极其耗时，效率较低。
Double square root (DSR) equation has provided a new theoretical framework for developing wave equation migration.
双平方根(dsr)方程为波动方程偏移提供了一种新的理论框架。
Therefore, the wave equation pre-stack depth migration, a method starting directly from the rolling surface, is discussed.
为此，探讨了直接从起伏地表开始的波动方程叠前深度偏移方法。
Prestack depth migration is an optimal imaging method for PSV wave.
叠前深度偏移是转换波最佳成像方法。
In this paper a fitting decomposition method is proposed and the principles for construe - ting equations which characterize the absorbing boundary conditions is discussed for wave equation migration.
本文讨论了在波动方程偏移问题中构造吸收边界条件方程的原则，并提出了求解具有吸收边界条件的偏移问题的一种新方法——矩阵拟合分解方法。
Wave equation migration after common receiving point slant stacks (WEMCRPSS) is essentially a prestack migration method.
共接收点倾斜叠加波动方程偏移，本质上是一种叠前偏移方法。
On the basis of the finite element solution to elastodynamic problems, we propose a new method of finite element elastic wave migration.
本文在弹性动力学问题的有限单元解的基础上，提出了一种弹性波偏移的新方法——有限单元法弹性波偏移。
Since the one way wave equation modeling scheme can be considered as the inverse depth migration, we can use the current depth migration schemes and its codes.
单程波算法可视为深度偏移的“逆运算”，这样可以很好地借用已知的深度偏移方法及其程序系统。
The seabed terrain, sand wave migration and the growth of regional erosion ditch create subsea pipeline suspended span.
沙波沙脊区海底管线悬跨的产生，主要是海底地形、沙波的移动和区域性冲沟的发育所造成的。
Although the wave field based pre-stack depth migration is the most reliable method for complex structure imaging, it has a high computation cost and a poor adaptation to geometry.
基于波场延拓的叠前深度偏移是实现复杂构造地质体成像的可靠方法，但存在着计算量大、对观测系统适应性差等缺点。
This paper points out the mistake occurring in studying seismic wave by optical method and analyses the current migration theory and methods.
本文指出用物理光学的研究方法来研究地震波时所存在的问题。讨论了目前偏移的理论和方法。
This essentially is the very reason why the effect of wave equation migration is undesirable at present moment.
这正是目前波动方程偏移效果不太理想的根本原因。
It is shown in real data processing that the method not only reduces arc phenomenon in migration but also removes particular multiple reflection wave.
实际资料应用表明，该方法不仅能减少倍移“画弧”现象，而且在消除特殊的多次波方面也有明显效果。
In wave equation migration using finite element method, a great deal of computer's internal storage and computer time are used because of too many unknowns involved.
在使用有限元法求解波动方程偏移过程中，由于未知量数目巨大，需要花费大量的计算机存储空间和计算时间。
Applications of plane wave migration method and their effectiveness on common shot gathers and common offset gathers are also presented.
给出了平面波偏移方法在共炮点道集和共偏移距道集数据上的应用以及效果评价。
We proposed residual migration velocity analysis by synthetic source records based on residual migration velocity analysis in the plane wave domain.
本文在平面波剩余速度分析方法的基础上提出了基于波动理论的合成震源记录剩余偏移速度分析方法。
A new coordinate transform is here introduced to obtain a new family of wave equation migration algorithms.
本文提出一个新的坐标又换，可得到一套新的波动方程偏移算法。
Taking aim at solving the important velocity model problem in wave equation pre-stack depth migration, This paper studies the method and software of building 3d migration velocity model.
针对波动方程叠前深度偏移中重要的速度模型问题，研究了一套三维速度建模方法和软件。
The result showed that the illuminated weighting imaging results by wave equation prestack depth migration from relief surface very coincide with the structural configuration of model.
结果表明：起伏地表波动方程叠前深度偏移照明加权成像结果与理论模型构造形态非常吻合。
The 3-D wave equation prestack depth migration is one of the most important techniques in the structure imaging and the inversion of elastic parameters of complex media.
三维波动方程叠前深度偏移是复杂介质中进行构造成像、弹性参数反演的重要环节。
Plane wave has the overall direction, compared with the normal migration, the plane-wave imaging results can be comparable to, and has a high computational efficiency.
平面波具有全局方向性，相对逐炮偏移而言，平面波偏移成像的结果是可以与其相相比的，并有很高的计算效率。
Plane wave has the overall direction, compared with the normal migration, the plane-wave imaging results can be comparable to, and has a high computational efficiency.
平面波具有全局方向性，相对逐炮偏移而言，平面波偏移成像的结果是可以与其相相比的，并有很高的计算效率。
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