3-D multi-parameter type traveltime tomography in a spherical coordinate frame: comparison of double and triple class simultaneous inversions

It is now common practice to perform simultaneous traveltime inversion for the velocity field and the reflector geometry in reflection/refraction tomography, or the velocity field and the hypocenter locations in regional earthquake tomography, but seldom are all three classes of model parameters updated simultaneously. This is mainly due to the trade-off between the different types of model parameters and the lack of different seismic phases to constrain the model parameters. Using a spherical-coordinate ray tracing algorithm for first and later(primary reflected) arrival tracing algorithm in combination with a popular linearized inversion solver, it is possible to simultaneously recover the three classes of model parameters in regional or global tomographic studies. In this paper we incorporate the multistage irregular shortest-path ray tracing algorithm(in a spherical coordinate system) with a subspace inversion solver to formulate a simultaneous inversion algorithm for triple model parameters updating using direct and later arrival time information.Comparison tests for two sets of data(noise free and added noise) indicate that the new triple-class parameter inversion algorithm is capable of obtaining nearly the same results as the double-class parameter inversion scheme. Furthermore,the proposed multi-parameter type inversion method is not sensitive to a modest level of picking error in the traveltime data, and also performs well with a relatively large uncertainty in earthquake hypocentral locations. This shows it to be a feasible and promising approach in regional or global tomographic applications.     

3-D simultaneous inversion for velocity and reflector geometry using multiple classes of arrivals in a spherical coordinate frame

The two key requirements in conducting 3-D simultaneous traveltime tomography on real data at the regional and global scale with multiple classes of arrival time information are (1) it needs an efficient and accurate arrival tracking algorithm for multiply transmitted, reflected (or refracted) and converted waves in a 3-D variable velocity model with embedded velocity discontinuities (or subsurface interfaces), and (2) a subdimensional inversion solver is required which can easily search for different types of model parameters to balance the trade-off between the different types of model parameter updated in the simultaneous inversion process. For these purposes, we first extend a popular grid/cell-based wavefront expanding ray tracing algorithm (the multistage irregular shortest-path ray tracing method), which previously worked only in Cartesian coordinate at the local scale, to spherical coordinates appropriate to the regional or global scale. We then incorporated a fashionable inversion solver (the subspace method) to formulate a simultaneous inversion algorithm, in which the multiple classes of arrivals (including direct and reflected arrivals from different velocity discontinuities) can be used to simultaneously update both the velocity fields and the reflector geometries. Numerical tests indicate that the new inversion method is both applicable and flexible in terms of computational efficiency and solution accuracy, and is not sensitive to a modest level of noise in the traveltime data. It offers several potential benefits over existing schemes for real data seismic imaging.     

数据域初至波走时与成像域反射波走时联合层析速度建模方法

复杂地表探区,尤其是盆山过渡区的油气勘探是我国也是世界上油气勘探的重点区域,但是此类区域油气地震勘探中满足精确地震成像的速度建模一直是个没有很好解决的问题.本文提出了一种综合性的数据域初至波走时与成像域反射波走时联合层析复杂地表浅中深层速度建模方法,并针对联合层析速度反演解的非唯一性问题,深入地分析了层析反演中正则化的本质意义,指出了建立构造特征正则化方法的具体技术路线,提出了联合层析的实现流程及策略.理论和实际数据试验表明,本文提出的数据域初至走时与成像域反射走时联合层析浅中深层速度建模技术避免了常规建模方法中浅层速度模型与中深层速度模型的融合问题,较好地解决了传统成像域反射层析对近地表模型的不可控更新问题,整体提升了深度域浅中深层速度模型的建模精度,进而提高了复杂地表、复杂构造区的地震成像质量.     

球坐标系下多震相走时三参数同时反演成像

球坐标系下多震相走时三参数(速度、震源位置和反射界面)同时反演需要解决两个关键问题:(1)球坐标系下3D速度模型中多次透射、反射(折射)及转换波精确、快速的射线追踪;(2)同时反演时三种不同参数间的强耦合问题.为此,我们将直角坐标系下分区多步不规则最短路径算法推广至球坐标系中,进行区域或者全球尺度的多震相射线追踪.然后将其与适合多参数同时反演的子空间算法相结合,形成一种球坐标系下联合多震相走时三参数同时反演的方法技术.与双参数(速度和反射界面或速度和震源位置)同时反演的数值模拟对比分析显示:三参数与双参数的同时反演结果大体接近,并且它们对到时数据中可容许的随机噪声不太敏感.结果说明本文中的同时反演成像为一种提高成像分辨率,同时反演速度、震源位置和反射界面的有效方法.     

变阻尼约束层析成像及其在VSP资料中的应用(英文)

初至波走时层析成像已经取得了广泛的应用,然而,由于观测系统的限制,射线在模型中分布不均匀,导致层析结果的分辨能力不足。变阻尼约束方法应用不均匀的先验信息来匹配不均匀的数据分布,可以减小速度模型校正量与射线覆盖程度的相关性。本文将变阻尼约束方法应用于初至波旅行时层析成像中,并将平滑约束方法加入正则化方程组中来避免单独使用变阻尼约束带来的不稳定性,利用阿尔法滤波器对反演中间迭代结果进行平滑和去噪,采用LSQR算法求解线性方程组来提高收敛速度和压制误差传递。本文应用上述层析成像算法对VSP观测系统进行速度反演,分别应用于检测板速度模型数据和实际VSP资料速度反演中,结果表咀变阻尼约束层析成像可以改善射线不均匀覆盖带来的影响,从而提高速度反演结果的质量;VSP资料检波点附近的速度反演结果可靠性高。     

天山-准噶尔地区地震层析成像与壳幔结构

通过对东西天山两条天然地震剖面的远震P波与近震P波走时资料以及2001-2007年新疆地方台网的近震走时资料分析,获得了天山-准噶尔地区的三维地震层析图像.层析反演使用的台站数140个,地震事件1132个,P波走时数24904条.检测板试验结果指出,东西天山剖面、天山轴部和东准噶尔地区P波速度扰动恢复能力相对高.纵波波...     

应用地震层析成象技术研究深部速度结构

罗马尼亚Ｖａｎｃｅａ地震区是大陆上发生与板块磁撞和削减有关的中深部地震活动的地区之一。本文介绍了应用地震层析成象方法研究该地区深部速度结构成果。在研究中使用了地方和区域地震所记录的４３３个浅源和中部地震的到时资料反演求解深至２００ｋｍ的三维速度结构,在走时和射线路径的计算中利用了有效的三维射线跟踪技术,在反演中采用ＬＳＱＲ算法,高分辨率的地震层析图象揭示了速度结构的广泛不均匀性,结果表明,地震层析     

非线性层析反演速度建模技术

深度速度模型的构建仍然是地震成像中的巨大挑战,获得一个精确的深度速度模型和减少深度成像项目周期都是至关重要的。常规层析反演速度建模每次迭代相当于一次线性反演,且需要重新的拾取工作,导致非常耗时,效率低下。本文提出非线性层析反演速度建模技术来建立速度模型。拾取共成像点道集的RMO量,转换到叠前域,作为运动学不变量,通过层析反演迭代进行模型更新。用一个多次的线性反演来逼近一个非线性的物理过程,避免重复的拾取工作,大大提高项目的运转效率。通过实例证明该方法的有效性。      

密度和速度随机分布共网格模型的重力与地震联合反演

针对重力与地震联合反演存在的问题,结合已有的研究成果,本文研究实现了速度和密度随机分布共网格单元模型的建模技术,以适应密度和速度剧烈变化的复杂模型及联合反演的计算要求.重力正演利用了该网格的二度半体模型,并进一步改进了地震走时的二维射线追踪计算方法,以适用于速度随机分布的网格介质.结合改进的模拟退火算法,实现了这种共网格条件下的重力与地震资料的同步联合反演.模型试验证明了重力与地震联合反演可以准确确定复杂物性界面的密度和速度结构,适用于物性界面不完全一致和物性变化剧烈的复杂模型,并且联合反演结果要优于单独的重力反演.带先验信息约束下的实际资料的联合反演,进一步证明了该方法的适用性和效果,可提高反演精度并减少多解性.     

多震相菲涅耳体射线走时同时反演成像

高频假设下的地震射线理论以及相应的地震成像理论表明,在射线稀疏条件下,不可能得到较高分辨率的构造成像;而有限频射线理论更符合实际地震的传播规律,即地震波的走时不仅与中心射线(传统的几何射线)上的速度分布有关,而且与中心射线附近一定范围(称其为第一菲涅耳体)内的速度异常分布有关.鉴于此,本文提出了计算多震相地震波菲涅耳体有限频射线的方法,并定义了走时敏感核函数,同时给出了利用多震相菲涅耳体有限频射线进行速度模型和反射界面同时反演成像的公式.利用多震相走时资料,使用传统射线层析成像方法与有限频射线层析成像方法进行了速度和界面的同时反演成像.结果表明,当射线密度较小时,无论是对速度模型的重建还是对反射界面几何形状的更新,有限频射线层析成像方法均优于传统射线层析成像方法, 而变频有限频射线层析成像则是实际地震层析成像的首选反演算法.      

重震反演中国东北地壳上地幔三维密度结构

本文利用重力和地震P波到时数据反演得到了中国东北地区地壳上地幔三维密度结构.与单一的重力或地震反演相比,重震反演一方面有效地克服了重力反演结果垂向分辨率低的问题,另一方面也提高了地震反演结果的可靠性.结果显示:中国东北地区的地壳及上地幔剩余密度异常分布与构造单元具有明显的相关性,造山带对应低密度异常,盆地对应高密度异常;区域内火山下方有明显的低密度体存在,可能是由于太平洋板块俯冲进入上地幔并部分滞留,在滞留板块深部脱水和软流圈热物质共同作用下产生了上涌岩浆,喷发后形成了火山.     

背景噪声面波与布格重力异常联合反演:山西断陷带三维地壳结构

讨论了利用面波与布格重力异常联合反演三维地壳速度结构的新方法,并利用该方法联合反演获得山西断陷带地壳S波速度结构.通过建立速度与密度之间的经验关系,利用非线性迭代反演方法获得最终速度模型.结果显示,联合反演获得的速度模型可以同时提高对面波及重力数据的观测拟合程度,而面波单独反演得到的速度模型则无法很好的拟合重力观测数据.相比较,联合反演速度模型中的大同火山区中下地壳的低速异常幅值小于面波单独反演模型中低速异常体的幅值.联合反演速度模型结果揭示,吕梁山地区在中下地壳存在低速异常,并且和北部的大同火山区低速异常相连接,说明可能导致新生代以来大同火山区岩浆活动的上地幔构造活动(上地幔局部上涌,地幔柱)可能对山西断陷带的形成和构造活动起到了一定的控制作用,并且导致了吕梁山地区中下地壳的低速异常.     

基于多震相联合反演江苏地区一维速度模型研究

利用地震走时数据,采用联合反演方法获取了江苏地区的一维P波速度模型。与仅采用初至波走时的传统天然地震走时获取方法相比,该方法充分利用了大量存在的续至波参与反演,能有效改进中下地壳的反演能力。针对地震震相目录中常存在震相标识错误的问题,采用的自动判别筛选震相方法能最大限度提高数据走时的精度,可以对不同震相进行有效区分。与其他常用一维速度模型相比,本文反演的模型对Pg、Pn震相走时拟合效果最佳,残差最小。当所用走时数据拥有较高定位精度时,该反演方法能为研究区三维速度结构成像和地震定位提供较可靠的一维速度模型。     

地震层析成像技术在岩体完整性测试中的应用

地震波层析成像借鉴了医学上X射线断面扫描的基本原理,利用地震波穿过地质体后走时及能量的改变等物理信息,通过数学处理重建地质体内部图像,从而得到所研究地质体的岩性及构造分布。本文利用这种方法,在一个钻孔中利用电火花震源激了弹性波,在另一个钻孔布设多个检波点同时接收,拾取弹性波初至时间,将接收到的数据利用SIRT方法进行反演迭代计算,最终形成一个弹性波速度谱图,然后利用岩土体的弹性波速度差异推断岩体完整性分布。与其它测试方法比较,该方法分辨率高,空间位置准确,在工程物探、岩土工程勘察中具有较好的应用前景。     

海洋拖缆地震资料初至波走时层析反演

初至波走时层析反演技术作为建立近地表速度模型的重要手段,是解决陆地资料复杂静校正问题的关键技术。而折射波广泛发育的海洋地震资料,对折射波信息的关注与运用并没有得到广泛的重视。本文首次将层析反演方法应用于海洋拖缆地震数据的近海底速度模型的建立。本文方法与陆地资料层析反演的主要区别在于:①在震源信号的最小相位化处理后进行初至时间的拾取,避免了混合相位子波初至拾取不准带来的误差;②以海水深度与海水速度作为反演约束条件,减小了迭代误差。实测二维资料的层析反演结果表明,本文方法可反演出较为精确的海洋地层速度结构。      

Tomographic determination of 3－D crustal structure──Joint inversion of explosion and earthquake data

Ｔｏｍｏｇｒａｐｈｉｃｄｅｔｅｒｍｉｎａｔｉｏｎｏｆ３－Ｄｃｒｕｓｔａｌｓｔｒｕｃｔｕｒｅ──Ｊｏｉｎｔｉｎｖｅｒｓｉｏｎｏｆｅｘｐｌｏｓｉｏｎａｎｄｅａｒｔｈｑｕａｋｅ　ｄａｔａＸｉａｎ－ＫａｎｇＺＨＡＮＧ（张先康）；Ｚｈｕｏ－ＸｉｎＹＡＮＧ（杨卓...     

Tomographic determination of 3-D crustal structure — Joint inversion of explosion and earthquake data

In this paper, the theory and method, obtaining the tomographic determination of three-dimensional velocity structure of the crust by use of the joint inversion of explosion and earthquake data, are given. The velocity distribution of the crust is regarded as a continuous function of the spatial coordinates without parametrization of the velocity model ahead, so that the inversion solution would not be influenced by different parametrization procedures. The expressions of integration kernels, which relates the two kinds of data sets, are also given. The authors have processed the observed data in Tangshan earthquake region by the method proposed in this paper, and obtained the tomographic results of the middle and upper crust structures in this region. The comparison of these results with the result obtained only by the explosion data, has also been made.     

First‐arrival traveltime tomography with modified total‐variation regularization

First‐arrival traveltime tomography is a robust tool for near‐surface velocity estimation. A common approach to stabilizing the ill‐posed inverse problem is to apply Tikhonov regularization to the inversion. However, the Tikhonov regularization method recovers smooth local structures while blurring the sharp features in the model solution. We present a first‐arrival traveltime tomography method with modified total‐variation regularization to preserve sharp velocity contrasts and improve the accuracy of velocity inversion. To solve the minimization problem of the new traveltime tomography method, we decouple the original optimization problem into the two following subproblems: a standard traveltime tomography problem with the traditional Tikhonov regularization and a L₂ total‐variation problem. We apply the conjugate gradient method and split‐Bregman iterative method to solve these two subproblems, respectively. Our synthetic examples show that the new method produces higher resolution models than the conventional traveltime tomography with Tikhonov regularization, and creates less artefacts than the total variation regularization method for the models with sharp interfaces. For the field data, pre‐stack time migration sections show that the modified total‐variation traveltime tomography produces a near‐surface velocity model, which makes statics corrections more accurate.     

Iterative tomographic analysis based on automatic refined picking

The ever-growing size of data sets for active and passive seismic imaging makes the availability of automatic procedures for rapid analysis more and more valuable. Such procedures are especially important for time-critical applications like emergency decisions or re-orienting of ongoing seismic surveys. In this paper a new, iterative scheme for 3D traveltime tomography is presented. The technique, based on a tool originally developed for earthquake data, uses cross-correlation to examine waveform similarity and to adjust arrival times on seismic sections. A preliminary set of reference arrival times is first corrected by the cross-correlation lag and then used to build an initial 3D tomographic velocity model through a standard inversion code; traveltimes calculated from this model are then taken as new reference arrivals and the process of pick adjustment is repeated. The result is a tomographic image, upgraded and refined at each iteration of the procedure. The test performed on the waveform data set recorded during the 2001 SERAPIS active seismic survey in the gulfs of Naples and Pozzuoli (Southern Italy) shows that the 3D iterative tomography scheme produces a velocity image of the structure of the Campi Flegrei caldera which is consistent with the results from previous studies, employing just a fraction of the time needed by a human analyst to identify first breaks. We believe that this technique can be effectively employed for rapid analysis of large data-sets within time-critical or time-dependent tasks and for automatic 4D tomographic investigations.     

Seismic tomography constrained by bouguer gravity anomalies: Applications in western Washington

Tomographic inversions for velocity variations in western Washington indicate a high correlation with surface geology and geophysical measurements, including gravity observations. By assuming a simple linear relationship between density and velocity (Birch's law) it is possible to calculate the gravity field predicted from the velocity perturbations obtained by local tomographic inversion. While the predicted gravity matches observations in parts of the model, the overall correlation is not satisfactory. In this paper we suggest a method of constraining the tomographic inversion to fit the gravity observations simultaneously with the seismic travel time data. The method is shown to work well with synthetic data in 3 dimensions where the assumption of Birch's law holds strictly. If the sources of the gravity anomalies are assumed to be spatially localized, integration can be carried out over a relatively small volume below the observation points and sparse matrix techniques can be applied. We have applied the constrained inversion method to western Washington using 4,387 shallow earthquakes, to depths of 40.0 km, (36,865 raypaths) convering a 150×250 km region and found that the gravitational constraints may be satisfied with minor effect on the degree of misfit to the seismic data.