共查询到20条相似文献，搜索用时 156 毫秒
1.
李献智 《地震地磁观测与研究》1995,16(1):15-19
应用一种新思路、新方法研究兴都库什－贝加尔地震带内的地震迁移，结果表明，地震沿地震带由南西西向北东东方向定向迁移，平均迁移速度为每年１２９ＫＭ量级与中国大陆西部地震带（区）的地震迁移速度相当，研究结果为地震动力学和地震预报提供了一定的依据。 相似文献
2.
根据滇西地震带大理－剑川段地震活动特征，把公元１４９８－１９９１年Ｍ≥４．７级地震迁移分为４期。每期地震迁移均为洱源地区的地震为先导，洱源先导地震震级越大，全段地震活动水平就越高，反之亦然。文中从地下水对断裂的弱化的角度，讨论了地震迁移规律及原因。洱源地区地下水对其断裂弱化的程度最高，其断裂最薄弱。这样，在区域应力场的作用下，最薄弱的洱源地区必将首先破裂而发震，所以每期地震迁移均以洱源地区的地震为 相似文献
3.
李献智 《地震地磁观测与研究》1995,(1)
应用一种新思路、新方法研究兴都库什－贝加尔地震带内的地震迁移，结果表明，地震沿地震带由南西西向北东东方向定向迁移，平均迁移速度为每年１２９ｋｍ，量级与中国大陆西部地震带（区）的地震迁移速度相当．研究结果为地震动力学和地震预报提供了一定的依据． 相似文献
4.
根据滇西地震带大理─剑川段地震活动特征，把公元１４９８～１９９１年Ｍ≥４．７级地震迁移分为４期。每期地震迁移均以洱源地区的地震为先导，洱源先导地震震级越大，全段地震活动水平就越高，反之亦然。文中从地下水对断裂的弱化的角度，讨论了地震迁移规律及原因。洱源地区地下水对其断裂弱化的程度最高，其断裂最薄弱。这样，在区域应力场的作用下，最薄弱的洱源地区必将首先破裂而发震，所以每期地震迁移均以洱源地区的地震为先导。认为洱源地区的地震活动特征可以作为预测全段地震活动水平的“窗口”，大理地区在今后５年左右的时间内（即１９９６年前后）有发生６级左右地震的可能性。 相似文献
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本文研究了日本内陆及其外围海域发生大地震后的地震活动迁移现象。在所研究的6个震例中,一个共同的特点是,地震活动的迁移总是沿着地壳内的活动地质构造带发生。有时可以根据地震活动的迁移来进一步确定活动构造带的存在。把板块边缘地区的地震活动类比为沿着力学偶合平面迁移和扩散,我们可以认为,岛上的活动构造带对应着地壳块体的力学相互作用边界。地震迁移的形式可能不只一种。在我们所研究的震例中发现了以下特征:地震迁移速度约为几km/年;大地震震源区之间存在着地震空区;在每一条地震带上有一定的地震活动周期。地震迁移的一种可能机制是:由于地壳块体的相对运动,在其边界上的凹凸不平区造成了构造应力集中,这些凹凸不平区相继地发生破裂,形成了地震迁移。 相似文献
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日本海－鄂霍次克海深震带地震活动与中国大陆地震有一定的相关性，尤其是其地震迁移规律与中国大陆展布方向相同的地震带的迁移规律一致，因此，所得结果不仅对预测中国大陆地震大形势有意义，而且也找到了两者力学上的联系。 相似文献
7.
日本海－鄂霍次克海深震带地震活动与中国大陆地震有一定的相关性，尤其是其地震迁移规律与中国大陆展布方向相同的地震带的迁移规律一致，因此，所得结果不仅对预测中国大陆地震大形势有意义，而且也找到了两者力学上的联系。 相似文献
8.
地震活动迁移是地震群体活动的一个特征，它可以反映地震构造带活动特点及其地震动力作用概况。本文研究了青藏块本及其周边地区强震空间分布随时间变化的规律，发现自１８９７年以来地震活动有自南而北，再由北向南的往返迁移规律，而且这种迁移与地震活跃期有明显的对应关系，在此基础上，讨论了本区地震动力作用演变及发展，进而对本区第Ｖ地震活跃期今后几年地震活动发展的趋势进行了判断。 相似文献
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鲜水河断裂带地震活动特征及强震发生随时间增长概率 总被引：3，自引：0，他引：3
作者等仔细分析了鲜水河断裂带从１７２５年到现在的地震资料，并利用乌莫洛夫Ｔ─Ｓ、Ｍ为参数的作图法及强震发生随时间增长概率，绘制了地震活动图件及地震发生概率曲线以及Ｍ─Ｔ图和鲜水河断裂应变释放曲线。根据这些资料可以清楚地看出鲜水河断裂带自１７２５年到现在可分为两个大的活动周期，其中６．０级以上地震有由康定依次向甘孜迁移的特点。在每一个大的地震活动周期中，地震基本上两次重复由康定向甘孜迁移的过程，而且较强地震多发生在第二次迁移过程中，１９８２年甘孜地震标志着断裂带在第二幕地震活动高潮中，中强震已经完成了最后一次由断裂带东南端向西北端迁移的过程。同时考虑到断裂带应变释放曲线的特征，估计鲜水河断裂带目前已进入新的平静阶段。前两个大的活动周期之间，平静了近一个世纪。按历史上地震定向迁移规律，估计在新的活动期地震仍将从康定方向开始，逐步向甘孜发展。 相似文献
10.
应用地震综合效应场函数方法，对地震前的空区、条带及大地震的迁移现象，根据强震前地震活动的四要素，进行了计算，其预报效果令人满意。 相似文献
11.
On the aperture effect in 3D Kirchhoff-type migration 总被引：5，自引：0，他引：5
Jianguo Sun 《Geophysical Prospecting》1999,47(6):1045-1076
It is well known that the migrated image given by a Kirchhoff-type (diffraction-stack) migration with limited aperture is always accompanied by some events which depend on the migration aperture. Although these events may severely affect the quality of migration, they have been studied only in 2D cases. Here, the events due to the migration aperture in 3D situations are investigated using a new method of analysing the reconstructed wavefield. It is found that a finite migration aperture results in a reconstructed wavefield with two components. One comes from the tangent points and curves between the traveltime surfaces of reflected and point-diffracted rays and is independent of the migration aperture, and the other is from the boundary of the migration aperture and depends strongly on the location and size as well as on the shape of the migration aperture. It is this last component that describes the aperture effect in migration. If the migration aperture is not sufficiently large, and if the input for migration is not zero on the boundary of the migration aperture, the boundary component may partially or totally cancel the migration signal. Furthermore, for synthetic data, the aperture effect cannot be eliminated by enlarging the migration aperture because, except for the common-shotpoint data, the aperture effect always exists however large the migration aperture becomes. This leads to the conclusion that the published Kirchhoff-type operators are not the exact inverse operators of the Fresnel–Kirchhoff integral if the input data are synthetic. 相似文献
12.
A.J. Berkhout 《Geophysical Prospecting》2017,65(1):106-145
Surface removal and internal multiple removal are explained by recursively separating the primary and multiple responses at each depth level with the aid of wavefield prediction error filtering. This causal removal process is referred to as “data linearization.” The linearized output (primaries only) is suitable for linear migration algorithms. Next, a summary is given on the migration of full wavefields (primaries + multiples) by using the concept of secondary sources in each subsurface gridpoint. These secondary sources are two‐way and contain the gridpoint reflection and the gridpoint transmission properties. In full wavefield migration, a local inversion process replaces the traditional linear imaging conditions. Finally, Marchenko redatuming is explained by iteratively separating the full wavefield response from above a new datum and the full wavefield response from below a new datum. The redatuming output is available for linear migration (Marchenko imaging) or, even better, for full wavefield migration. Linear migration, full wavefield migration, and Marchenko imaging are compared with each other. The principal conclusion of this essay is that multiples should not be removed, but they should be utilized, yielding two major advantages: (i) illumination is enhanced, particularly in the situation of low signal‐to‐noise primaries; and (ii) both the upper side and the lower side of reflectors are imaged. It is also concluded that multiple scattering algorithms are more transparent if they are formulated in a recursive depth manner. In addition to transparency, a recursive depth algorithm has the flexibility to enrich the imaging process by inserting prior geological knowledge or by removing numerical artefacts at each depth level. Finally, it is concluded that nonlinear migration algorithms must have a closed‐loop architecture to allow successful imaging of incomplete seismic data volumes (reality of field data). 相似文献
13.
Geological interpretation based on gravity gradiometry data constitutes a very challenging problem. Rigorous 3D inversion is the main technique used in quantitative interpretation of the gravity gradiometry data. An alternative approach to the quantitative analysis of the gravity gradiometry data is based on 3D smooth potential field migration. This rapid imaging approach, however, has the shortcomings of providing smooth images since it is based on direct integral transformation of the observed gravity tensor data. Another limitation of migration transformation is related to the fact that, in a general case, the gravity data generated by the migration image do not fit the observed data well. In this paper, we describe a new approach to rapid imaging that allows us to produce the density distribution which adequately describes the observed data and, at the same time, images the structures with anomalous densities having sharp boundaries. This approach is based on the basic theory of potential field migration with a focusing stabilizer in the framework of regularized scheme, which iteratively transfers the observed gravity tensor field into an image of the density distribution in the subsurface formations. The results of gravity migration can also be considered as an a priori model for conventional inversion subsequently. We demonstrate the practical application of migration imaging using both synthetic and real gravity gradiometry data sets acquired for the Nordkapp Basin in the Barents Sea. 相似文献
14.
本文介绍一种基于τ-P变换的新的叠后深度偏移方法。这一方法是在均匀介质条件下根据波动方程推导出的。其基本思想是:在τ-p域中,当波场分解为它的平面波成分时,改变其τ、p值,再通过τ-p反变换回到深度域中,从而完成了地下界面的偏移归位。 方法所需的计算时间基本是与完成τ-p正、反变换所需时间相同,是一种快速的偏移方法。它可用于任意形状的地下界面,甚至在强干扰背景的条件下,也能提高资料的信噪比和改善信号的连续性。这一方法是在深度域中进行τ-p变换,故它能适应速度存在纵、横变化的地区。为了论证本方法的效果,本文给出了不同的正演理论模型和偏移结果的例子。 相似文献
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Planform dynamics of the Iquitos anabranching structure in the Peruvian Upper Amazon River 
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下载免费PDF全文 Alejandro Mendoza Jorge D. Abad Christian E. Frias Collin Ortals Jorge Paredes Hugo Montoro Jorge Vizcarra Cesar Simon Gabriel Soto‐Cortés 《地球表面变化过程与地形》2016,41(7):961-970
The upper reach of the Amazon River has a very dynamic morphology, with the highest rates of migration observed in the entire Amazon River. It has an anabranching channel pattern which alternates between a condition of single channel and anabranching structures; in particular, the anabranching structure near Iquitos City shows an interesting channel behavior. Its channels migrate at different rates, where there are processes of narrowing and widening, and also collision and development of new channels. The temporal evolution of the Iquitos anabranching structure is described during the period from 1985 to 2014. The study is carried out by using satellite images to track the migration patterns, which are contrasted to the underlying geological units in the valley. Bathymetry of the structure and several velocity transects were obtained during a field campaign prior to the 2012 historic flood event. This information allowed for numerical modeling in order to compute the hydrodynamic flow field that complements the temporal analysis, aiming to understand the planform migration patterns after the 2012 flood event. It is observed that the geological units play an important role in modulating the migration rates and planform development of the channels. The channels in the structure are in contention to be the main channel, which become the secondary channel after migration. This causes the channels to experience a rise in bed elevation and narrowing of the channel itself; if this trend continues for several more years, these channels will detach from the Iquitos anabranching structure, thus forming paleo‐channels. This geomorphic process is important for horizontal and vertical soil heterogeneity along the floodplain. In general, the analysis shows a complex interaction between the underlying geological units, flow structure, morphology of the bed and planform migration. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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The state-of-the-art joint migration inversion faces the so-called amplitude-versus-offset challenge, due to adopting over-simplified one-way propagation, reflection and transmission operators to avoid over-parameterization in the inversion process. To overcome this challenge, we apply joint migration inversion to horizontally layered media (or 1.5-dimensional media) and parameterize the solution space via density and velocity models. In this scenario, one-way propagation, reflection and transmission operators required by the joint migration inversion process can be analytically and correctly derived from the subsurface models, so the amplitude-versus-offset challenge is successfully overcome. We introduce a new concept, which is named ‘inverse propagation’, into our 1.5-dimensional amplitude-versus-offset joint migration inversion. It can correctly reconstruct subsurface wavefields by using a surface-recorded receiver wavefield with all the influence of transmission, reflection and multiples accounted for. A synthetic example is used to demonstrate the correctness of the inverse propagation. This work is the foundation to further develop the 1.5-dimensional amplitude-versus-offset joint migration inversion technology. 相似文献
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提出了一种新的偏移速度分析方法——基于控制照明的合成震源记录交互剩余偏移速度分析方法．与其他类似偏移速度分析方法的不同点在于：（1） 叠前深度偏移采用基于波动理论的快速合成震源记录算法;（2）偏移方法采用平面波震源,与速度分析方法一致;（3）应用控制照明技术,避免了因横向变速而导致的平面波震源波场在传播过程中的畸变,从而减小了速度分析的误差;（4）实用的速度谱设计,使交互偏移速度分析可行且易于操作．模型和新疆实际资料的试算表明该方法是一种有效和实用的偏移速度分析方法． 相似文献
19.
矢量波场弹性波Kirchhoff偏移 总被引：2，自引：0，他引：2
Based on Kuo and Dai＇s vectorial wave-field extrapolation equations, we derive new Kirchhoff migration equations by introducing unit vectors which represent the ray directions at the imaging points of the reflected P- and PS converted-waves. Furthermore, using the slope of the events on shot records and a ray racing procedure, mirror-image reflection points are found and the reflection data are smeared along the Fresnel zone. The migration method proposed in this paper solves two troublesome imaging problems caused by limited receiving aperture and migration artifacts resulting from wave propagation at the velocities of non original wave type. The migration method is applied successfully with model data, demonstrating that the new method is effective and correct. 相似文献
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地震波干涉偏移和偏移反演成像是近年来十分活跃的两个研究领域.干涉偏移提供了一个新的地震波数据成像工具,而偏移反演则提供了高逼近度地震成像.二者的共同目的是改善传统直接偏移方法的成像效果,展宽成像区域并提高成像的分辨率.本文研究干涉偏移方法和偏移反演方法对于地震成像效果的影响,探讨二者在提高成像分辨率上的异同.对于偏移反演,通过建立正则化模型,研究了预条件共轭梯度迭代正则化方法及改进措施,并通过绕射点模型数值模拟验证了该方法比直接偏移能够提高振幅的保真度和成像的分辨率.对于干涉偏移和偏移反演这两种方法,对层速度地震模型进行了数值模拟.结果表明干涉偏移和偏移反演成像方法比传统的偏移方法在成像效果上是更加有效的,因而对于实际的地震成像问题很有应用前景. 相似文献