利用深反射地震数据构建的多阶面波频散曲线反演近地表横波速度结构——以跨班公湖—怒江缝合带深反射地震资料为例

深反射地震剖面法为了获取深部结构特征常常采取大的偏移距采集数据.目前公开发表的相关资料中,鲜有利用深反射地震炮集数据获取近地表的结构特征.为此,本文通过正演测试了相关数据处理流程,即利用有限差分正演了起伏地表模型的大偏移距地震单炮弹性波场特征,通过共检波点域面波信号F-K频谱叠加构建新方法,从深反射地震数据集中提取了高品质的多阶面波频散曲线,再利用多阶面波联合反演获得了近地表的结构特征.在前述正演流程基础上,利用跨越班公湖—怒江缝合带的SinoProbe深反射地震剖面中的实际炮集数据,求取了基阶和一阶瑞利波频散曲线,联合反演后得到近地表横波速度结构.该结果与初至波走时反演获取的纵波速度结构具有较好的一致性,且在近地表的浅层分辨率较纵波速度结构特征更高,而更与已有地质认识相吻合.本文提供的相关数据处理流程表明利用深反射地震炮集数据,也能够获取近地表浅层的横波速度结构.     

一种起伏地表条件下的照明补偿方法

起伏的地表条件限制了采集孔径范围并造成深层地震照明不足,为改善该类地区的成像质量,本文提出了一种起伏地表条件下的照明补偿方法.首先,基于小波束波场延拓算子和逐步累加的外推方法在波场延拓过程中解决起伏地表面的影响,并引入空间滤波函数压制虚拟层内的偏移噪音;其次,利用局部指数标架对上、下行波场分解,得到局部角度域成像和照明补偿因子.再次,利用计算出的成像值和照明补偿因子,在局部倾角域完成照明补偿.SEG起伏地表模型测试证明了本方法的有效性,深层构造照明度明显加强,不同角度成像振幅更加均衡,该技术为提高起伏地表地区的成像品质提供了新的手段.     

基于信号估计的高分辨率叠加速度分析

如何得到高分辨率的叠加速度谱是高分辨率地震资料处理的关键.本文在分析地震共中心点(CDP)道集的振幅随偏移距变化(AVO)特性的基础上,提出一种信号模型来逼近CDP道集,然后利用优化技术估计信号,并采用信号估计误差实现信号检测,从而提出一种新的基于信号检测和估计的高分辨率叠加速度谱分析方法.文中的方法充分利用地震信号波形中所包含的速度信息.     

基于平均速度分析的近地表纵波速度反演

面波频散曲线对于横波速度、纵波速度、层厚等近地表地球物理参数的敏感度相差较大,现阶段通过频散曲线可以获得较为精确的近地表横波速度与厚度信息,但无法直接对纵波速度进行反演.研究表明,泊松比对于波长(W)-探测深度(D)关系较为敏感.基于这一发现,本文根据频散曲线与反演获取的横波速度结构计算平均速度,获取W-D关系曲线.但合成数据测试证明,因近地表浅层对应的W-D曲线变化较小,且浅层纵波速度反演不准确会使误差累积,直接反演W-D曲线无法获取可靠的纵波速度剖面.本文改进了基于平均速度分析的近地表纵波速度反演方法,在目标函数中加入了对浅层信息较为敏感的W/D-D信息,同时对W-D曲线与W/D-D曲线进行联合反演.合成数据测试证明可以获取较为准确地浅层与深层纵波速度.将该方法应用于实际地震数据中,联合反演得到的纵波速度剖面与微测井数据较为吻合,证明本文提出的方法可以不借助其他信息,仅通过面波频散信息,获取更为准确地近地表纵波信息.     

基于波场延拓的变换坐标转换波静校正

常规的转换波静校正的基本思想都是从地震波的运动学特征出发,基于地表一致性假设.在地表条件复杂和地表高程相差较大的地区,它不仅无法解决严重的静校正问题,反而会带来新的畸变.本文基于频率波数域波动方程偏移原理,采用波场延拓方法实现转换波静校正,其关键点在于时间空间域和频率波数域的相对应.文中通过坐标变换将起伏地表转化为新坐标系下的水平地表,把炮点和检波点映射到同一水平面上,然后在新坐标系下推导频率域波动方程延拓公式,接着对下行波P和上行转换波SV分别利用近地表速度向上延拓到基准面,恢复起伏地表到基准面之间的真实波场,最后转换到原始坐标系取出基准面数据完成转换波静校正.通过对模拟和实际数据处理,证明该方法是正确和有效的.     

起伏地表下的直接叠前时间偏移

提出了一种新的叠前时间偏移方法和流程,可不必应用野外静校正,直接对起伏地表采集的地震数据进行叠前时间偏移.本文采用输入道成像方式,通过基于稳相点原理给出单道数据的走时和振幅计算方法,发展了一个表驱动的叠前时间偏移算法.偏移方法可依据同相轴是否被拉平确定叠加速度和修正近地表速度模型,也可依据拟成像的构造倾角,自适应地确定偏移孔径;后者既减少了偏移计算量,也压制了偏移噪声.文中用二维起伏地表的断陷盆地模型的理论数据验证了所发展方法的成像效果.     

潜水波层析成像速度建模技术在鄂尔多斯黄土塬区的应用研究

针对鄂尔多斯盆地西缘黄土塬区复杂地表和复杂地下构造导致难以准确成像问题,采用浅层潜水波层析反演（DWT）速度建模技术,同时辅以中深层反射波层析成像技术,形成一套实用叠前深度偏移速度建模方法。首先生成一个基于钻井和解释信息的起始近地表速度,其次利用潜水波层析反演建立初始近地表模型,将其与常规处理获得的中深层速度模型进行匹配拼接,建立起初始的起伏地表全速度模型,然后在此基础上利用基于反射波的网格层析进行中深层速度建模,经过多轮次迭代,最终获得可靠的高精度速度模型。鄂尔多斯盆地西缘MJT工区地震资料的成像处理验证了这一套速度建模技术的有效性,地下构造成像更合理也更精确。      

利用初至波走时速度成像进行近地表静校正的方法

提出了一种利用常规地震初至波走时速度成像进行近地表静校正的方法。该方法的基础是回折波射线的走时层析成像，它能准确地求出近地表连续速度分布，用浅层速度成像结果能够得到准确的近地表静校正量。文中给出了初至波走时射线层析成像的理论模型试验结果，成像是令人满意的。     

波动方程基准面延拓研究进展

复杂的地表采集条件是地震偏移成像必须面对的问题．地形高程起伏变化较大,以及近地表低速层速度的横向变化,是导致反射地震数据非双曲时差特征的主要原因,严重影响了后续速度估计和偏移成像的精度．对于复杂地表条件,基于地表一致性的时移法静校正很难满足高精度资料处理的要求．波动方程基准面延拓方法不受地表一致性限制,很好地保持了波传播的动力学特征,而且在改善成像质量方面效果显著,应用广泛．本文探讨了消除地表因素影响的基准面延拓方法,对一些意义比较突出的方法进行了详细介绍．     

基于双曲线校正的偏移距VSP速度分析

本文引入了一种VSP速度估算方法——基于双曲线校正的VSP速度分析方法,它将VSP记录沿反射波射线路径按时间外推成地面地震记录,然后利用上行波,按地面双曲线公式,给定一系列叠加速度,在共炮点道集内进行速度扫描,制作叠加速度谱,然后根据动校正结果的好坏,来估算地层的均方根速度.这种方法与常规的利用下行直达波计算速度相比,可以获取视观测井段以下的地层速度,并且获取的速度与地面地震的叠加速度一致,有机地将VSP与地面地震结合起来.     

GPR velocity determination by image-wave remigration

We have studied in detail the theoretical and numerical properties of a finite-difference algorithm for image-wave time-remigration. For a number of synthetic models, numerical experiments have been performed. For these examples, we obtained perfect agreement between the theoretical predictions and numerical results. The examples also prove the computational efficiency of the algorithm. An application to ground-penetrating-radar (GPR) data demonstrates that image-wave remigration can be used to estimate models with laterally varying velocities. The quality of the latter is confirmed by a final zero-offset time migration.     

鄂尔多斯块体及其东南缘剪切波速度结构与波速比研究

利用深源远震的纯S波波形拟合方法研究了鄂尔多斯块体及其东、南缘的剪切波速度结构。结果显示，鄂尔多斯块体内部榆林台站下方速度结构相当稳定，没有很明显的高低速层变化，随着深度的增加，剪切波速度稳步升高；在该台下方25km深处有一个厚度达12km的层位(ys=3．90km／s)，该层的波速度相对其东部同等深度处的波速度偏低(以≥4．00km／s)。鄂尔多斯地块东部边缘的地壳厚度都比榆林厚，而且呈现高、低速层相间结构，低速层明显增多，与块体内部比较一致的特征为下地壳是一个厚达10km的速度较低的下地壳(yS=3．8km／s)，但埋深在35km左右。另外反演得到了各个台站的P波速度结构，并对相应的波速比(Vp/Vs)进行了研究，发现位于鄂尔多斯块体内部的榆林台波速比平均值仅为1．68，上地壳波速比处在非常低的状态(1．60左右)，中下地壳一直到上地幔的波速比稳定在1．73左右，反映介质均匀稳定，处于一种刚性状态；而鄂尔多斯块体东、南边缘的台站，都有几个波速比较高(1．80左右)的层位，其中东部边缘苛岚和离石地区的波速比平均值系统超过一般的弹性体波速比平均值1．732，反映了边缘地区地壳活动相对比较活跃，介质层中可能有其他物质的影响。     

Study on Shear Wave Velocity Structure and Velocity Ratio Beneath Ordos Block and Its Eastern and Southern Margins

Using pure S wave fitting method, we studied the shear wave velocity structures under the Ordos block and its eastern and southern marginal areas. The results show that the velocity structure beneath Yulin station in the interior of Ordos block is relatively stable, where no apparent change between high and low velocity layers exists and the shear wave velocity increases steadily with the depth. There is a 12km thick layer at the depth of 25km under this station, with an S wave velocity (Vs=3.90km/s) lower than that at the same depth in its eastern and southern areas (Vs≥4.00km/s). The crust under the eastern margin of Ordos block is thicker than that of the Yulin station, and the velocity structures alternate between the high and low velocity layers, with more low velocity layers. It has the same characteristic as having a 10km-thick low velocity layer (Vs=3.80km/s) in the lower crust but buried at a depth of aout 35km. Moreover, we studied the Vp/Vs ratio under each station in combination with the result of P wave velocity inversion. The results show that, the average velocity ratio of the Yulin station at the interior of Ordos block is only 1.68, with a very low ratio (about 1.60) in the upper crust and a stable ratio of about 1.73 in the mid and lower crust, which indicates the media under this station is homogenous and stable, being in a state of rigidity. But at the stations in the eastern and southern margins of the Ordos block, several layers of high velocity ratio (about 1.80) have been found, in which the average velocity ratio under Kelan and Lishi stations at the eastern margin is systemically higher than that of the general elastical body waves (1.732). This reflects that the crust under the marginal areas is more active relatively, and other materials may exist in these layers. Finally, we discussed the relationship among earthquakes, velocity structures beneath stations and faults.     

伽师强震群区上地壳三维速度层析成像——人工爆破和天然地震的联合反演

伽师震区位于天山褶皱、帕米尔构造弧与塔里木块体三个构造单元的交接地带,近年来该区发生了一系列的强震活动.为进一步获得该震区详细的地壳速度结构,本文利用人工爆破和天然地震资料联合反演的方法,对1997年新疆伽师震区布设的三维人工地震透射台阵和流动地震台网的资料进行处理,重建了台阵下方上地壳三维速度扰动图像,并结合地震活动分布,对伽师强震群的地震成因作出进一步分析.结果表明研究区上地壳速度结构在纵向和横向上具有明显的非均匀性,随着深度的逐渐加深,震区下方以萨如锡为中心的低速异常体逐步被高速异常体所替代.自12 km深度开始,在与强震群震中相应的位置上,明显出现沿北北西向的高P波速度异常体,在其周围为相对低速分布,呈现出低速条带环绕高速条带的分布格局,V_P/V_S在相同的位置上也表现为高值分布.这种结构上的差异可能与伽师强震群发生有密切关系.16 km深度的P波速度层析图表明,伽师强震群发生在地壳相对高速扰动区内或是高速扰动向低速扰动过渡的边缘,壳内高速体的存在为强震的孕育和发生提供了重要基础.     

天山中部地壳及上地幔三维速度层析成像

应用新疆区域台网记录的地震资料,结合前人对新疆速度结构研究的结果作为初始模型,利用地震层析成像的方法反演了天山中部地壳及上地幔三维速度结构。三维图像结果显示：天山中部地区波速呈现出不均匀性,45km深度以上各层波速表现出高速性质,45km以下的区域波速却表现出低速性质;纬向剖面显示出0～40km深度范围内波速起伏较大,而40km深度以下速度相对稳定。     

热水条件下花岗质糜棱岩的摩擦滑动实验研究

为了探讨大陆地壳断层深部的力学性质,我们选择了采自红河断裂带的糜棱岩作为实验样品,进行热水条件下的高温高压摩擦滑动实验.实验在一个以气体为介质的高温高压三轴实验系统中进行.实验条件是：有效正应力为200 MPa;孔隙水压为30 MPa（在400 ℃到600 ℃之间为超临界水条件）;温度为100 ℃到600 ℃;轴向加载的速率范围从0.04 μm/s到0.2 μm/s再到1 μm/s.实验结果表明：（1）当温度小于300 ℃时,糜棱岩的摩擦强度随着温度的上升而增大;当温度大于300 ℃时,糜棱岩的摩擦强度随着温度的上升而减小.这种趋势和以往花岗岩的摩擦滑动数据基本一致;（2）糜棱岩在200 ℃和400 ℃时表现为速度弱化,其余温度下为速度强化;（3）糜棱岩与已有花岗岩的摩擦滑动数据并不完全一致;（4）花岗质糜棱岩速度弱化向速度强化转变的温度在430 ℃附近,以此我们可以推测：在变形机制为摩擦滑动的深部条件下,地震成核的深度范围可以比以往的估计更深.     

同一台基的强震仪记录与地震仪记录对比研究

本文根据时域实时方法,对辽宁省共同台基的数字宽频带加速度记录和地震仪速度型记录进行相互仿真,并做了对比分析。结果表明,可以由加速度记录仿真得到真实的速度与位移时程;同样,地震仪速度型记录通过仿真也能得到加速度时程。由此可见,强震观测和地震观测在一定范围内是可以相互替代的。     

Geometrical characteristics of phase and group velocity surfaces in anisotropic media

The phase and group velocity surfaces are essential for wave propagation in anisotropic media. These surfaces have certain features that, especially, for shear waves result in complications for modelling and inversion of recorded wavefields. To analyse wave propagation in an anisotropic model, it is important to identify these features in both the phase and group domains. We propose few characteristics for this analysis: the energy flux angle, decomposed in the polar and azimuth angle correction angles and enhancement factor, which is able to characterize both singularity points and triplication zones. The very simple equation that controls the triplications is derived in the phase domain. The proposed characteristics are illustrated for elastic and acoustic anisotropic models of different symmetry classes.     

The crust and upper mantle structure beneath southern Italy by earthquakes and DSS data

This paper describes a travel—time analysis performed for the Italian seismic stations, in particular those operating in southern Italy, in order to study the crust and upper mantle properties in the region. Average P-wave residuals of teleseisms in the distance range 30°–95° with respect to Jeffreys-Bullen tables, at thirteen permanent and temporary stations of southern Italy, are coherent with a high velocity zone beneath Calabria and northern Sicily and low velocity material in the mantle beneath the Eolian Islands. Travel—time residuals from Tyrrhenian intermediate earthquakes show a high velocity structure which extends in a NW direction from a depth of at least 200 km down to 450 km.A damped least-squares inversion applied to DSS data confirms the existence of low velocity zones in the crust beneath the Eolian Islands, at 8–12 km depth, that agrees with previous results and with the lack of S waves from local earthquakes.Publication No. 193, Progetto Finalizzato Geodinamica, CNR-Roma.     

Constrained tomography of realistic velocity models in microseismic monitoring using calibration shots

The knowledge of the velocity model in microseismic jobs is critical to achieving statistically reliable microseismic event locations. The design of microseismic networks and the limited sources for calibration do not allow for a full tomographic inversion. We propose optimizing a priori velocity models using a few active shots and a non‐linear inversion, suitable to poorly constrained systems. The considered models can be described by several layers with different P‐ and S‐wave velocities. The velocities may be constant or have 3D gradients; the layer interfaces may be simple dipping planes or more complex 3D surfaces. In this process the P‐ and S‐ wave arrival times and polarizations measured on the seismograms constitute the observed data set. They are used to estimate two misfit functions: i) one based on the measurement residuals and ii) one based on the inaccuracy of the source relocation. These two functions are minimized thanks to a simulated annealing scheme, which decreases the risk of converging to a local solution within the velocity model. The case study used to illustrate this methodology highlights the ability of this technique to constrain a velocity model with dipping layers. This was performed by jointly using sixteen perforation shots recorded during a multi‐stage fracturing operation from a single string of 3C‐receivers. This decreased the location inaccuracies and the residuals by a factor of six. In addition, the retrieved layer dip was consistent with the pseudo‐horizontal trajectories of the wells and the background information provided by the customer. Finally, the theoretical position of each calibration shot was contained in the uncertainty domain of the relocation of each shot. In contrast, single‐stage inversions provided different velocity models that were neither consistent between each other nor with the well trajectories. This example showed that it is essential to perform a multi‐stage inversion to derive a better updated velocity model.