多尺度逐次逼近退火遗传算法反演地壳速度结构

根据多尺度逐次逼近思想,建立了多尺度逐次逼近退火遗传算法.该方法能有效地解决遗传算法中存在的收敛"早熟"问题.采用该方法对一个高速异常体进行了数值模拟试验,并对青藏高原东北缘阿尼玛卿缝合带东段上部地壳速度结构实际资料进行了处理,结果表明,多尺度逐次逼近退火遗传算法能够较好地应用于地震走时层析成像研究.     

阿尼玛卿缝合带及两侧上地壳泊松比分布

本文通过对马尔康－古浪宽角反射和折射剖面高精度观测段（200～400 km）的Pg、Sg资料的分析解释,给出了该区段上地壳速度结构和泊松比分布.并利用震相识别误差分析、分辨率计算及不同初始模型筛选等方法,使走时反演结果的可靠性进一步提高.研究表明：对应于阿尼玛卿缝合带的275km～355 km桩号段内平均泊松比高达0.297,P波和S波速度呈横向高低速条带变化,库赛湖－玛沁断裂和舟曲－两当断裂基本上均位于高泊松比和低速带内,并分别处在缝合带与若尔盖盆地和西秦岭褶皱带的分界上.阿尼玛卿缝合带南侧的若尔盖盆地平均泊松比较低,约为0.257,北侧西秦岭褶皱带的平均泊松比为0.264.     

由多震相走时和波形作三维地震成像

本项成果包括：提出天然地震走时反演层析成像技术,采用下列方法使得处理结果得以改善：１）利用３２个地震,４０４条射线的Ｐｇ,Ｓｇ,Ｐｍ,Ｓｍ,Ｐｎ,Ｓｎ等震相增加约束条件：２）用已有精度较高的人工地震测深化结果作速度约束;３）用波形反演来修改模型,把波源,介质吸收,散射等物理特征集中反映在记录中,把诸多物理量开发出来互为约束,以修改后的模型再作反演,使解的稳定性大大提高;４）采用最优化过程,选择遗传     

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.     

多尺度全变分法及其在时移地震中的应用

本文针对时间推移地震本身包含不同时期的两次或者两次以上的勘探反问题,构造了一种快速有效的反演方法——多尺度全变分法.通过引入全变分正则化来代替传统的Tikhonov正则化,针对待反演参数不连续的情况,提高了算法精度.为了提高计算效率,引入了多尺度方法,从而构造了多尺度全变分方法.在数值模拟中,针对一个时间推移地震反演问题对多尺度-Tikhonov正则化法、单一尺度全变分法、以及本文所构造的多尺度全变分法进行了比较.结果表明,本文所提出的多尺度全变分法是一种稳定、快速和精确的反演方法.     

利用地震走时反演阿尼玛卿缝合带东段及两侧基底结构

对11炮宽角地震反射/折射的Pg波走时数据进行了反演,结果表明:阿尼玛卿缝合带东段基底速度结构整体呈低速带分布,两侧的速度分布相对均匀;缝合带内基底界面剧烈下凹,最深达5.5 km,不存在稳定的基底界面;松潘-甘孜微块体基底界面整体埋深达3.5 km,相对平坦,其中部略微下凹;从缝合带过渡到西秦岭褶皱带,基底界面急剧抬升至1.8 km,之后迅速下降至4.7 km,然后趋于平坦;缝合带的地壳变形存在挤压和走滑两种形式,在缝合带及邻近地区,上部地壳物质曾有过向北方向逃逸的迹象.     

阿尼玛卿缝合带东段上地壳结构-马尔康-碌曲-古浪深地震测深剖面结果

位于青藏高原东北缘川北甘南地区的马尔康——碌曲——古浪深地震测深剖面穿越阿尼玛卿缝合带东段,利用该剖面获得的Pg, Sg初至折射波资料,采用有限差分成像、射线追踪反演、时间项反演和走时曲线分析等方法,对阿尼玛卿缝合带东段及其两侧的上地壳结构进行了分析. 结果表明, 研究区基底变化较大. 由南向北,基底在若尔盖盆地呈稳定的上隆状态,在阿尼玛卿缝合带内强烈下陷,在缝合带北侧一定范围内隆升之后,向北呈下陷趋势. 阿尼玛卿缝合带相对两侧整体表现为南倾的低速带结构,且内部速度存在非均匀性. 库赛湖——玛沁断裂、武都——迭部断裂和舟曲——两当断裂均表现为不同规模的低速带. 库赛湖-玛沁断裂和舟曲——两当断裂位置处基底界面埋深有明显变化,是区隔阿尼玛卿缝合带南北两侧的主要断裂. 武都——迭部断裂发生在基底界面深度变化带上,它与舟曲——两当断裂可能具有同一深部构造背景. 阿尼玛卿缝合带所呈现的强烈下陷的基底低速结构和非均匀性体现了上地壳受挤压的破碎结构特征.     

小波变换多尺度地震波形反演

完全非线性地震波形反演问题是石油地球物理勘探领域中一个非常重要而又难度很大的问题。本文提出了多尺度地震波形反演的小波变换方法,对于一维非线性地震波形反演问题,将该方法和已有的简单迭代法及多重网格法作了比较,数值实验结果表明,本方法效果较好。     

阿尼玛卿缝合带东段地壳结构的接收函数研究

沿四川红原至甘肃武威一线布设了20个宽频带地震台站, 在一年的观测时间里共接收到81次远震记录, 利用台站记录的远震P波波形数据和接收函数方法, 获得了沿测线的接收函数剖面、 每个台站下方的S波速度结构. 研究结果表明, 研究区地壳速度结构复杂, 整个地壳的平均S波速度偏低. 在四川阿坝弧形断裂——秦岭地轴北缘断裂之间, 地壳中10~40 km的深度范围内普遍存在低速层, 是阿尼玛卿古特提斯洋从闭合、 斜向碰撞到俯冲板块折返或逆冲岩片抬升等复杂地质过程所形成的构造特征. 沿剖面莫霍面深度约为50 km, 南边略深北边略浅.      

小波变换多尺度地震波形反演

完全非线性地震波形反演问题是石油地球物理勘探领域中一个非常重要而又难度很大的问题。本文提出了多尺度地震波形反演的小波变换方法,对于一维非线性地震波形反演问题,将该方法和已有的简单迭代法及多重网格法作了比较,数值实验结果表明,本方法效果较好。     

2D multiscale non-linear velocity inversion

An efficient and robust non-linear inversion method for velocity optimization combining a global random search followed by a simplex technique is presented. The background velocity field is estimated at different spatial scales by analysing image gathers after iterative prestack depth migrations. First, the global random search is used to determine the main features/trends of the velocity model (large-scale component). Then, the simplex technique improves the resolution of the velocity field by estimating smaller-scale features. A measure of the quality of the velocity model (objective function) is based on flattening offset events in depth-migrated image gathers. To help constrain the solution, the algorithm can incorporate a priori information about the model and a smoothness condition. This 2D velocity estimation offers the benefit of being semi-automatic (requiring minimal human intervention) as well as providing a global and objective solution (which is a useful approach to an interpretation-derived velocity-estimation technique). The method is applied to a real data set where AVO analysis is carried out after prestack depth migration, as structural effects are non-negligible. It is demonstrated that the method can successfully estimate a laterally inhomogeneous velocity model at a computational cost modest compared with an interpretation-based iterative prestack depth velocity-analysis technique.     

地层衰减对地震波速度逆散射反演的影响研究

在利用地震波数据进行地球物理反演时,地层对地震波的吸收衰减效应会对地层物性参数的准确反演产生较大的影响,因此利用黏弹性声波方程进行反演更符合实际情形.本文在考虑地层衰减效应进行频率空间域正演模拟的基础上,提出基于黏弹性声波方程的频率域逆散射反演算法并对地震波传播速度进行反演重建,在反演过程中分别用地震波传播复速度和实速度来表征是否考虑地层吸收衰减效应.基于反演参数总变差的正则化处理使反演更加稳定,在反演中将低频反演速度模型作为高频反演的背景模型进行逐频反演,由于单频反演过程中背景模型保持不变,故该方法不需要在每次迭代中重新构造正演算子,具有较高的反演效率;此外本文在反演过程中采用了基于MPI的并行计算策略,进一步提高了反演计算的效率.在二维算例中分别对是否考虑地层吸收衰减效应进行了地震波速度反演,反演结果表明考虑衰减效应可以得到与真实模型更加接近的速度分布结果,相反则无法得到正确的地震波速度重建结果.本文算法对复杂地质模型中浅层可以反演得到分辨率较高的速度模型,为其他地震数据处理提供比较准确的速度信息,在地层深部由于地震波能量衰减导致反演分辨率不太理想.     

Appraisal problem in the 3D least squares Fourier seismic data reconstruction

Least squares Fourier reconstruction is basically a solution to a discrete linear inverse problem that attempts to recover the Fourier spectrum of the seismic wavefield from irregularly sampled data along the spatial coordinates. The estimated Fourier coefficients are then used to reconstruct the data in a regular grid via a standard inverse Fourier transform (inverse discrete Fourier transform or inverse fast Fourier transform). Unfortunately, this kind of inverse problem is usually under‐determined and ill‐conditioned. For this reason, the least squares Fourier reconstruction with minimum norm adopts a damped least squares inversion to retrieve a unique and stable solution. In this work, we show how the damping can introduce artefacts on the reconstructed 3D data. To quantitatively describe this issue, we introduce the concept of “extended” model resolution matrix, and we formulate the reconstruction problem as an appraisal problem. Through the simultaneous analysis of the extended model resolution matrix and of the noise term, we discuss the limits of the Fourier reconstruction with minimum norm reconstruction and assess the validity of the reconstructed data and the possible bias introduced by the inversion process. Also, we can guide the parameterization of the forward problem to minimize the occurrence of unwanted artefacts. A simple synthetic example and real data from a 3D marine common shot gather are used to discuss our approach and to show the results of Fourier reconstruction with minimum norm reconstruction.     

Effect of non-linear soil–structure interaction on seismic response of tall slender structures

Some structures may be very massive and may have to be located on relatively soft soil. In such cases, the soil adjacent to the structure behaves in a non-linear fashion and affects the response of the structure to the dynamic loading. An approximate hybrid approach to analyse soil–structure systems accounting for soil non-linearities has been developed in this paper. The approach combines the consistent infinitesimal finite-element cell method (CIFECM) and the finite-element method (FEM). The CIFECM is employed to model the non-linear (near-field) zone of the soil supporting the structure as a series of bounded media. The material properties of the bounded media are selected so that they are compatible with the average effective strains over the whole bounded medium during the excitation. The linear zone of soil away from the foundation, the far-field, is modelled as an unbounded medium using the CIFECM for unbounded media. The structure itself is represented by the FEM. The proposed method is used to model the dynamic response of a one-mass structure and a TV-tower supported on a homogenous stratum and excited by an earthquake. It was found that the secondary soil non-linearity might increase or decrease the base forces of tall slender structures depending on the type of structure, frequency content of the input motion and the dynamic properties of the near-field soil.     

华北三维虚波速度地震异常分析

基于华北地区1993～2002年发生的4068个地震的48120条模拟、 数字记录到时, 利用直达波射线方程反演进行三维虚波速度分析, 讨论了虚波速度变化的意义并探讨区域虚波速度演化与中强地震活动过程的关系。 研究结果表明, 中强地震多数发生在虚波速度的高、 低速度区的速度梯度带附近, 而且与地质构造条件有关。     

Three‐term inversion of prestack seismic data using a weighted l2, 1 mixed norm

We present a new inversion method to estimate, from prestack seismic data, blocky P‐ and S‐wave velocity and density images and the associated sparse reflectivity levels. The method uses the three‐term Aki and Richards approximation to linearise the seismic inversion problem. To this end, we adopt a weighted mixed l_{2, 1}‐norm that promotes structured forms of sparsity, thus leading to blocky solutions in time. In addition, our algorithm incorporates a covariance or scale matrix to simultaneously constrain P‐ and S‐wave velocities and density. This a priori information is obtained by nearby well‐log data. We also include a term containing a low‐frequency background model. The l_{2, 1} mixed norm leads to a convex objective function that can be minimised using proximal algorithms. In particular, we use the fast iterative shrinkage‐thresholding algorithm. A key advantage of this algorithm is that it only requires matrix–vector multiplications and no direct matrix inversion. The latter makes our algorithm numerically stable, easy to apply, and economical in terms of computational cost. Tests on synthetic and field data show that the proposed method, contrarily to conventional l₂‐ or l₁‐norm regularised solutions, is able to provide consistent blocky and/or sparse estimators of P‐ and S‐wave velocities and density from a noisy and limited number of observations.     

Assessment of the seismic non-linear behavior of ductile wall structures due to synthetic earthquakes

In this paper, different methods for generating synthetic earthquakes are compared in terms of related non-linear seismic response of ductile structures. The objective of the investigation is to formulate recommendations for the use of synthetic earthquakes for reliable seismic analysis. The comparison is focused on the accuracy of the reproduction of the characteristics of the structural non-linear response due to recorded earthquakes. First the investigations are carried out for non-linear single-degree-of-freedom systems. Later, the results are validated for a set of realistic buildings modelled as multi-degree-of-freedom systems. Various options of the classical stationary simulation procedure of SIMQKE and a non-stationary simulation procedure proposed by Sabetta and Pugliese are examined and compared. The adopted methodology uses a set of recorded earthquakes as a reference. Hundred synthetic accelerograms are generated for each examined simulation option with the condition that the related elastic responses are similar to those of the reference set. The non-linear single-degree-of-freedom systems are defined using six recognized hysteretic models and four levels of increasing non-linearity. The non-linear responses computed for the reference set and the studied simulation options are then statistically compared in terms of displacement ductility and energy. The results show that the implementation of the classical stationary procedure always leads to a significant underestimation of the ductility demand and a significant overestimation of the energy demand. By contrast, non-stationary time histories produce much better results. The results with the multi-degree-of-freedom systems are shown to confirm these conclusions.     

天山—帕米尔结合带的地壳速度结构及地震活动研究

利用流动地震台阵记录的地震数据,通过地震层析技术反演了天山—帕米尔结合带的P波速度结构,揭示出地壳结构的非均匀特征及其与地震活动的对应关系. 分析结果表明,天山和西昆仑的双向挤压导致塔里木西部边缘地壳严重变形,在山前地区形成基底隆起带,地壳深部则被断裂分割成为若干块体,有的块体可能卷入造山带内部;喀什坳陷地壳深部结构相对完整,变形程度较弱;天山和西昆仑的地壳结构显示出缩短增厚的波速特性,在与塔里木接壤的局部地区,壳幔边界附近存在热物质的侵入迹象. 大部分地震都发生在塔里木西部边缘的壳内高速块体周围,推测块体之间的相互作用和应力调整是导致天山—帕米尔结合带频繁发生地震的主要原因,伽师地震则与构造变形由天山向塔里木内部扩展以及该地区的地壳非均匀结构有关.     

菲涅耳体地震层析成像分辨率研究

层析成像分辨率的研究,不仅可以帮助分析层析方法的反演能力,评价层析反演的效果,还可以帮助指导层析参数设置,优化观测系统设计等.本文对比研究了前人提出的两种菲涅耳体层析成像分辨率的计算方法,并针对其存在的问题进行了优化.文中通过对二维理论模型的定量计算,总结了菲涅耳体地震层析成像分辨率的一些规律,并将其与射线层析的分辨率进行了对比.文中最后给出分辨率研究对观测系统与层析成像的指导作用,尤其是对层析中平滑窗设置、变网格层析中模型剖分原则给出了具体的建议.     

基于小波多尺度分析的奇性指数：一种新地震属性

传统的地震解释主要是观测地震振幅及相位的变化，但是地震振幅也会掩盖地下介质中真实的地质情况.在许多情况下，重要的地质信息可能是通过与振幅特征无关的奇异性参数来传递的.本文提出奇异性指数，即Hlder指数α（又被称为Lipschitz指数），可以作为一种新的地震属性，它能够准确反映数据中的奇点的位置和奇异性强度.Hlder指数α是对某一点上或某一点周围很小的范围内的奇异性强度的度量，大的α值表示低的奇异性（或高的正则性）.研究表明α可以作为一种自然的能够精确刻画地层边界的地震属性.本文根据这一思想，对合成和实测的地震数据进行了小波基础上的多尺度分析研究，结果表明由本文的算法得到的α提高了对地层边界划分的能力，而这些地层界面在传统的地震振幅显示则不明显.