基于独立分量分析的地震多次波压制的研究

1、基于独立分量分析的地震多次波压制的研究        【中文摘要】独立分量分析方法是近年发展起来的一种新的*信号处理方法，它在语音信号处理、生物医学信号处理、地震信号处理、以及移动通讯、图像处理等方面都具有非常重要的理论意义和实用价值，本文主要讨论其在地震信号处理中的应用。包括两个方面：在勘探地震记录中，一次波和多次波的分离；在自然地震记录中，针对沉积区接收函数中转换波信息和多次反射波信息的分离。传统的地学多次波压制技术多是基于输出信号能量最小的原则，这个原则是由二阶统计量推导而得到的。在多次波压制算法中，需要假设

2、一次波和多次波正交才可得到最优解，而这种假设往往并不符合地震勘探的实际情况。所以，本文针对以上这种传统多次波压制方法中所存在的缺陷，尝试将独立分量分析方法应用于地学多次波相减，这种方法的优点在于它是基于高阶统计量的，无需假设多次波和一次波正交，从而更符合地震勘探领域的实际应用条件。远震P波波形数据中包含了大量的地震台站下方地壳和上地幔速度中断面所产生的S P、P S P P等震相，然而，当地震台站位于较厚沉积层地区时，由于沉积层内形成的多次地震反射波振幅较强，且又与中断面产生的转换波在同一时段出现，就会将转换波信息沉没掉。目前，现有的技术手段很难将混合的转换波和多次反射波进行有效的分离，从而导

3、致在沉积区无法从接收函数中提取中断面信息。本文将尝试把独立分量分析方法应用于实现沉积层较厚区远震转换波与多次反射波的分离。');【Abstract】 Independent component analysis (ICA) derived from blind source separation (BSS) is a new method for finding underlying factors or components from multivariate (multidimensional) statistical data. The goal of ICA is to rec

4、over the unobserved source signals without any prior information given only the sensor observations that are unknown linear mixtures of the independent sources. Recently, because of a few assumptions on surroundings, ICA has become one of the exciting new topic, both in the field of data mining and

5、more generally in image processing, feature extraction, telecommunications, financial time series analysis.In the *, we mainly discuss its applications in the seismic signals processing, including the multiple attenuation in the records of seismic explosion and the separation of seismic converted-wa

6、ve and multiple reflected-waves in sedimentary basin.Seismic data is the important information resource of geological prospect and exploration. And the multiple reflections are often one of the most serious problems in seismic surveying which influence the authenticity and the reliability of seismic

7、 imaging badly and interfere the seismic interpretation, so as to increase the cost of seismic exploitation. At the present time, the methods of the multiple attenuation are divided into two categories. One is the filtering approaches based on the differences between the primary and the multiple. Th

8、e other is the prediction and subtraction approaches based on wave-equation. Without any a priori information and neither structural nor material information about the subsu*ce geology, the latter become an effective method and the main developing trend in the field of attenuating the multiple, and

9、that, more and more scholars realized that the subtraction step in the prediction and subtraction approaches based on wave-equation is the sticking point. The effective method of subtraction can not only solve the disaccord between the predictive multiple and the real multiple, but also reduce the c

10、omplex of calculation during the course of prediction largely. However, the energy minimum criterion (least-squares criterion) which is based on the second-order statistics is adopted by the almost existing multiple subtraction methods. From a theoretical point of view, only if the primary and the m

11、ultiple are normal, the multiple can be removed totally. But in general, the above assumption is invalid in the real seismic data, so that there will remain survival multiple in the primary which is induced by the optimal criterion based on second-order statistics.After working over a variety of the

12、 existing multiple attenuation methods and the ICA theory, we try to use the ICA technique for solving the problem of the multiple subtraction in order to hurdle the obstacle in the energy function based on second-order statistics. We view the seismic data and the predictive multiples as the observe

13、d signals, the primary and the real multiples as the source signals, so the subtraction can be treated as a processing of blind source separation. Because of no normal assumption in ICA technique, accordingly, we can settle the problem appeared in the second-order statistics method.In this *, the fr

14、ee-su*ce related multiple and the internal multiple are depicted for * out that the major amount of the multiple energy in seismic data is related to the large reflectivity of the free-su*ce. Next, it demonstrates the rationality of BSS equivalent to multiple subtraction theoretically and brings for

15、wards general ICA model for the real seismic data. At last, we use the synthetical data for validating the proposed method in this *. It makes the single trace as an example, deduces the time-distance equation of first-order free-su*ce related multiple, second-order free-su*ce related multiple and t

16、he primary of the first subsu*ce and the one of the second subsu*ce in detail. As a result, the two primaries are almost reserved absolutely. Therefore, the proposed method in this * is effective for the multiple attenuation.There are some strong velocity discontinuities or transitions in the earths

17、 curst and upper mantle, which can be recognized by tracing converted-wave phases in seismic wave records. However, when seismic stations are set in sedimentary area, the recorded converted-wave information will be masked by the recorded multiple reflected-waves caused by sedimentary formations. In

18、this case, it is hard to identify the velocity discontinuity from receiver function. Now there are not many effective methods to separate the mixed seismic converted wave and multiple reflected-waves. In this *, a new method is proposed based on Independent Component Analysis (ICA) to implement the

19、separation of seismic converted-wave and multiple reflected-waves recorded in sedimentary basin.On the base of analyzing the features of seismic signals, we do preliminary studies and try to apply ICA in seismic signals separation. We suppose that the seismic records of each station set in the sedimentary area are some linear mixture of seismic converted-wave and multiple reflected-wa