天然地震走时反演矩阵顺序三角化算法的优化和并行化

本文讨论了用于天然地震层析成像的矩阵顺序三角化算法,揭示了偏导数矩阵中非零元素的分布规律,在分析算法特点的基础上提出了对程序的几点优化措施,包括：采用合理的存储结构和计算次序以节省内存寻址时间;以一个一维数组存储上三角方阵以节省出一半的内存;对关键的Givens变换子程序进行优化和矢量化等,最终使程序的运行效率提高了数十倍.同时结合算法特点研究了矩阵顺序三角化的并行化方法,提出了两种并行化方案,在联想深腾6800超级计算机上实现了这两种并行算法;对计算量均衡等问题进行了讨论.     

复杂介质小波多尺度井间地震层析成像方法研究

复杂介质井间地震层析成像是一个很复杂的非线性反 演问题，常规的线性化反演方法无法得到好的解. 采用基于图形的弯曲射线追踪方法， 并将小波多尺度思想引入到井间层析成像，提出了小波多尺度井间地震层析成像方法，很好 地解决了非线性成像的难题，提高了图像的质量和分辨率. 物理模型实验结果表明， 该方法适合于复杂介质成像，并具有良好的实用性和效果.     

地震层析成像软件

GABWIT是应用地震体波走时资料、遗传算法反演地壳三维速度结构的软件,本介绍了该地震层析成像软件的主要功能以及技术特点,软件界面友好,功能齐全,适用性强,易于推广。     

地震层析成像研究的回顾与展望

对本世纪７０年代以来发展起来的地震层析成像研究及其在勘探地球物理领域的发展状况进行了简单的回顾,对地震层析成像研究今后的发展提出了开展多参数研究的设想,论述了地震层析成像研究中走时拾取、三维地震波场、三维地震时间场、广义线性反演解的分辨率问题以及重建图像的地质解释问题。     

井间地震资料测井约束层析成像

利用井间地震资料进行层析成像,由于受观测角的限制,其成像过程具有很强的不稳定性。为了提高成像过程的稳定性,本文将测井资料引入到反演过程中,利用测井资料约束井间地震反演成像过程。采用假设模型进行数值模拟和反演实验,并与无约束反演方法进行对比实验,多种反演结果对比表明,测井约束反演方法改善了层析成像过程的稳定性,提高了成像结果的精度。     

一种用于走时层析成像的改进算法

走时层析成像是根据首波走时重建声波、地震波或电磁波波速的层析技术，其所用到的射线路径依赖于波速分布。本文提出了一个依据费马原理寻找射线路径的新方法。费马原理指出，从发射点到接点的射线首波的走时极小，因此寻找射线路径的问题是一个最优化问题。     

新疆库车-克拉玛依地震层析成像

利用在同地区直接布设的观测台站,进行六个月连续观测所取得的地震数据,挑选清晰远震的Ｐ波到的数据,采用ＡＣＨ层析成像方法绘出了天山地区地壳和上地幔的三维速度图象,反演结果表明：天山南侧是塔里木地块高密度岩层产生的向北俯冲的高速体,天山北侧,准噶尔盆地内是产状较陡向南俯冲的高速体,天山主体就夹在两个俯冲带之间,形成一个不等边三角形的低速区,地壳范围是高速体和低速体的相间排列,与地表看到的地块的划分基本一致。在２００～３００ｋｍ的深度中,存在较大面积的低速体,低密度的热物质主要来源于幔,随着天山地区的强烈挤压与隆升,存在较大面积的低速体,低密度的热物质主要来源于地幔,随着天山地区的强烈挤压与隆升,深部热物质则向上迁移、渗透,甚至沿着断裂带达到上部地壳和地表。     

地震层析成像研究方法综述

国际上对地震层析成像的研究始于上世纪70年代末,经过30多年的发展,地震层析成像方法逐渐成熟,并越来越广泛地被运用到地球物理各个领域中.以地震层析成像方法的发展作为主线,主要介绍了地震层析成像方法和所用地震数据的发展.     

基于Matlab平台GUI的地震走时层析成像快速实现

地震走时层析成像是地球物理反演中的成熟方法之一,已在许多领域得到广泛应用,并取得了良好的效果。本文围绕地震走时层析成像GUI的快速实现,首先简要介绍了地震走时成像方法的原理和方法,并基于Matlab软件平台,利用GUI开发环境编写了二维横向非均匀地震走时层析成像图形用户界面(GUI),实现了方便快捷地反演地震测深资料的速度结构并以人机交互方式快捷灵活地将图像显示出来;结合实际观测资料处理结果表明,本文编制的GUI软件能够有效地实现地震走时层析成像结果的窗口化、图像化和快捷化。     

地震层析成像—地幔对流新模型的研究

利用地震层析成像数据计算地幔对流模型的方法。假设地幔地震层析成像数据对应的地幔横向不均匀结构是地幔热对流的结果，将地震层析成像数据转化为地幔温度不均匀分布。该方法考虑热流体动力学的3个基本方程，以及热输运方程中的非线性项，直接将上述地震层析成像转化的地幔温度不均匀分布作为内部荷载直接引入基本方程，进而反演计算地幔对流的基本格局。理论结果表明，对流格局不仅依赖地震层析成像数据，而且在很大程度上受地幔动力学框架和热动力参数（如Rayleigh数）以及边界条件和系统响应函数的影响。     

Applications of hybrid genetic algorithms in seismic tomography

Almost all earth sciences inverse problems are nonlinear and involve a large number of unknown parameters, making the application of analytical inversion methods quite restrictive. In practice, most analytical methods are local in nature and rely on a linearized form of the problem equations, adopting an iterative procedure which typically employs partial derivatives in order to optimize the starting (initial) model by minimizing a misfit (penalty) function. Unfortunately, especially for highly non-linear cases, the final model strongly depends on the initial model, hence it is prone to solution-entrapment in local minima of the misfit function, while the derivative calculation is often computationally inefficient and creates instabilities when numerical approximations are used. An alternative is to employ global techniques which do not rely on partial derivatives, are independent of the misfit form and are computationally robust. Such methods employ pseudo-randomly generated models (sampling an appropriately selected section of the model space) which are assessed in terms of their data-fit. A typical example is the class of methods known as genetic algorithms (GA), which achieves the aforementioned approximation through model representation and manipulations, and has attracted the attention of the earth sciences community during the last decade, with several applications already presented for several geophysical problems.In this paper, we examine the efficiency of the combination of the typical regularized least-squares and genetic methods for a typical seismic tomography problem. The proposed approach combines a local (LOM) and a global (GOM) optimization method, in an attempt to overcome the limitations of each individual approach, such as local minima and slow convergence, respectively. The potential of both optimization methods is tested and compared, both independently and jointly, using the several test models and synthetic refraction travel-time date sets that employ the same experimental geometry, wavelength and geometrical characteristics of the model anomalies. Moreover, real data from a crosswell tomographic project for the subsurface mapping of an ancient wall foundation are used for testing the efficiency of the proposed algorithm. The results show that the combined use of both methods can exploit the benefits of each approach, leading to improved final models and producing realistic velocity models, without significantly increasing the required computation time.     

基于声波测井资料的波动方程走时层析反演速度建模

地震勘探目标逐渐由浅层（< 2000 m）转向中深层（2000~3500 m）,高精度速度建模是实现精确地震成像的关键手段之一.目前,初至波或早至波速度层析建模方法已较为成熟,然而对深层速度建模更为重要的反射波层析建模方法依然面临走时拾取困难及计算量大等难题.针对当前中深层走时层析速度建模方法面临的难题,本文提出了一种基于声波测井资料的波动方程全波走时层析速度建模方法及策略.该方法首先通过早至波层析反演获得浅层及大尺度速度信息;其次,通过提取初次成像剖面的构造倾角信息,利用声波测井资料进行稀疏反演,进一步获得更高精度的速度模型;最后,以此为初始模型,进行全波层析反演获得最终偏移速度模型.数值结果表明,本文所提出的速度建模方法及策略不仅可以避免传统反射波层析建模方法因采用Born近似反偏移所带来的大计算量问题,且大幅提高了中深层速度建模的精度,进而能有效地提高中深层复杂构造区域的地震成像质量.

     

全球非均匀模型中的远震走时层析成像

远震走时层析成像是研究地球内部结构的重要工具. 通常, 远震走时层析成像使用一维地球参考模型计算研究区域外地震射线. 由于地球存在广泛非均匀结构, 传统远震走时层析成像在计算射线时忽略了研究区域外非均匀结构对射线的影响, 最终导致对研究区域内的成像结果产生影响. 为了减小模型外地球非均匀结构对远震走时层析成像的影响, 本文利用迎风差分格式数值求解程函方程, 得到全球非均匀模型中的远震射线, 以此为基础发展了基于全球非均匀模型的远震走时成像方法. 为了检验本文成像方法提升成像精度的有效性, 选取青藏高原东北缘为研究对象. 合成测试和实际数据成像结果显示, 在考虑地球非均匀结构以后, 成像结果更精确, 结果展现更多成像细节.

     

Joint inversion of travel times and waveforms by means of annealing algorithms. Application to a seismic refraction experiment

An algorithm of annealing is applied to a joint inversion of travel times and waveforms belonging to a synthetically generated seismic refraction experiment. The medium (crust and upper mantle) is modelled by a set of plane stratified layers and a halfspace. The obtained structure (elastic parameters and depth of layers) shows that, in spite of contaminating seismic noise and poor knowledge of the seismic source, annealing methods are a good tool in these kinds of inversion problems. We think that many characteristics of the annealing process described here could be used with real data and more sophisticated media for the crust and upper mantle of the earth than the present example.     

川西地区台阵环境噪声瑞利波相速度层析成像

2006年中国地震局地质研究所地震动力学国家重点实验室在川西地区(26°N~32°N,100°E~105°E)布设了由297台宽频带数字地震仪组成的流动观测台阵.利用该密集台阵29°N以北156个台站2007年1~12月份的地震环境噪声记录和互相关技术,我们得到了所有台站对的面波经验格林函数和瑞利波相速度频散曲线,并进一步反演得到了观测台阵下方2~35 s周期的瑞利波相速度分布图像．本文结果表明,观测台阵覆盖的川滇地块、松潘-甘孜地块和四川盆地的地壳速度结构存在显著差异,具体表现为：(1)短周期（2~8 s）相速度分布与地表构造特征相吻合,作为川滇地块、松潘-甘孜地块和四川盆地之间的边界断裂,龙门山断裂带和鲜水河断裂带对上述三个地块上地壳的速度结构具有明显的控制作用,四川盆地前陆低速特征表明相应区域存在较厚的（约10 km）沉积盖层;(2)中周期（12~18 s）相速度分布表明,川滇地块和松潘-甘孜地块中上地壳速度结构存在明显的不均匀横向变化,并形成了尺度不同且高、低速相间的分块结构,而四川盆地中地壳整体上已经表现出相对高速;(3)长周期（25~35 s）相速度分布表明,松潘-甘孜地块,特别是川滇地块中下地壳表现为广泛的明显低速异常,意味着它们的中下地壳相对软弱,而四川盆地的中下地壳呈现整体性的相对高速,意味着四川盆地具有相对坚硬的中下地壳,并且以汶川地震的震中为界,龙门山断裂带的地壳结构显示了北段为高速异常,南段为低速异常的分段特征．     

A new seismic hazard analysis using FOSM algorithms

From recent lessons, it is evident that earthquake prediction is immature and impractical as of now. Under the circumstances, seismic hazard analysis is considered a more practical approach for earthquake hazard mitigation, by estimating the annual rate of earthquake ground motions (or seismic hazard) based on seismicity and other geological evidences. Like other earthquake studies for the high-seismicity region around Taiwan, this study aims to conduct a new seismic hazard assessment for the region using the well-established FOSM (first-order second-moment) algorithm, on the record of 55,000 earthquakes observed in the past 110 years. The new seismic hazard analysis from a different perspective shows that the annual rate for earthquake-induced PGA to exceed the current design value (i.e., 0.23g) in two major cities in Taiwan should be relatively low, with it no greater than 0.0006 per year. Besides, the FOSM estimates were found very close to those with Monte Carlo Simulation (MCS), mainly because the skewness of the three random variables (i.e., earthquake magnitude, location, and model error) considered in the probabilistic analysis is not very large.     

基于FCM聚类约束的直流电阻率法与地震走时成像法二维联合反演

通过引入模糊均值聚类(FCM)模型约束函数对电阻率与速度进行约束,开展二维直流电阻率法与地震初至波走时成像法联合反演研究.在地下浅层结构勘探中,通常低电阻率的地质体具有低速特征,较高电阻率的地质体表现为较高的地震波速度.直流电阻率法因为低电阻率区域吸引电流而对其敏感,地震走时成像法因为射线集中在高波速区而对高速体敏感,因此,两者联合成像能够大幅度提高反演效果.合成数据反演表明,直流电阻率法和地震初至波走时联合反演对于两类地质体的分辨能力均有提升,能够优势互补.尤其是引入FCM模型约束进行联合反演,根据已知物性进行监督学习,进一步提高了反演质量,改善了成像模型的分辨率.

     

马尼拉俯冲带的地震层析成像研究

基于国际地震中心的P波走时数据和层析成像反演方法,获得了具有较高分辨率的马尼拉俯冲带的深部速度模型.结果表明,（1）高速的南海俯冲板片沿马尼拉俯冲带的俯冲形态随纬度发生变化,在14°N和16°N之间,板片俯冲角度较大,俯冲深度可达400~500 km,在17°N附近,俯冲板片角度和深度较南部变小,而在18°N附近,俯冲板片以近垂直角度俯冲到地幔转换带;（2）17°N和18°N之间俯冲角度的变化意味着南海板片发生了撕裂;（3）在14°N附近,南海板片由300 km以上的近垂直俯冲转为200~300 km深度的近水平展布,与震源分布存在较大的差异,表明南海板片发生了撕裂,并且导致410 km间断面抬升.根据成像结果计算的不同位置南海板片的俯冲长度和时间表明,南海板片俯冲之前的面积为现今面积的两倍,14°N最先开始发生俯冲,并由南向北扩展.     

Automating adjoint wave-equation travel-time tomography using scientific workflow

Recent advances in commodity high-performance computing technology have dramatically reduced the computational cost for solving the seismic wave equation in complex earth structure models. As a consequence, wave-equation-based seismic tomography techniques are being actively developed and gradually adopted in routine subsurface seismic imaging practices. Wave-equation travel-time tomography is a seismic tomography technique that inverts cross-correlation travel-time misfits using full-wave Fréchet kernels computed by solving the wave equation. This technique can be implemented very efficiently using the adjoint method, in which the misfits are back-propagated from the receivers (i.e., seismometers) to produce the adjoint wave-field and the interaction between the adjoint wave-field and the forward wave-field from the seismic source gives the gradient of the objective function. Once the gradient is available, a gradient-based optimization algorithm can then be adopted to produce an optimal earth structure model that minimizes the objective function. This methodology is conceptually straightforward, but its implementation in practical situations is highly complex, error-prone and computationally demanding. In this study, we demonstrate the feasibility of automating wave-equation travel-time tomography based on the adjoint method using Kepler, an open-source software package for designing, managing and executing scientific workflows. The workflow technology allows us to abstract away much of the complexity involved in the implementation in a manner that is both robust and scalable. Our automated adjoint wave-equation travel-time tomography package has been successfully applied on a real active-source seismic dataset.