用散射体波随机反演研究长白山火山区介质非均匀性

1、用散射体波随机反演研究长白山火山区介质非均匀性        观测和研究表明,地球内部存在着不同程度的介质非均匀性,由地震波所揭示的介质非均匀尺度可达8个数量级。根据散射体与地震波长之间的大小关系,将地球内部介质非均匀性分为两类:即大尺度非均匀性(长波长非均匀性)和小尺度非均匀性(短波长非均匀性)。在当代地震学中,用确定性方法研究大尺度非均匀性已是众所共知的事情,目前技术方法也已比较成熟；对小尺度非均匀性的研究则是一个全新的研究领域,其理论探索和方法研究还处于起步阶段,本文重点对3D小尺度介质非均匀性进行了研究。介

2、质非均匀性往往是地质构造运动的产物。研究地球内部介质的非均匀性,对于了解地球内部非均匀结构,特别是非均匀结构边界的产生过程、受力、变形及运动状态等对研究地球动力学、资源勘探、火山、地震观测预报均有重要的意义。论文主要研究内容及结论如下:1.利用统计学方法对随机介质模型进行了论述。论述了随机介质模型的建立方法、随机介质模型的类型及其特点;探讨了描述随机介质模型的两个主要参数(模型相关长度a、b和扰动标准差)和随机介质中的非均匀体之间的关系进行了讨论。2.论述了Von Karman型随机介质中S波包络展宽理论。基于双曲抛物线近似法研究了Von Karman型随机介质中S波包络展宽现象;探讨了Von

3、 Karman型随机介质非均匀性能量谱估计方法:分析了S波传播距离、激发源频率等对S波包络展宽的影响。3.论述了多层非均匀介质(非均衡随机介质)S波包络延时与随机介质模型参数之间的关系。通过等效传播长度将多层随机介质(各层具有不同的速度扰动率)转换为等效单层随机介质模型,建立了S波包络延时与随机介质模型参数之间的关系,为定量或定性描述介质非均匀性奠定了基础。4.采用有限差分法对二维Von Karman型随机介质中S波波场进行正演模拟,分析Von Karman型随机介质中S波包络线展宽现象,探讨了激发源的频率、介质速度扰动率及波传播的距离对S波包络线展宽的影响。5.采用S波包络峰值延时定性研究了

4、长白山天池火山区3D介质非均匀性。研究结果表明:长白山天池火山口地区地壳介质呈现强烈的横向和纵向非均匀性;天池火山口地区介质非均匀性具有多尺度特性或频率特性;介质非均匀性梯度带,是地震频发地带。6.采用S波包络延时定量研究了长白山天池火山区3D介质非均匀性。用Hurst指数k和log(?)(因模型速度扰动率和模型特征尺度相关距离a并不解耦)对介质非均匀性进行了定量描述。研究结果表明:天池火山口地区地壳介质呈现强烈的非均匀性;天池火山口地区介质非均匀性具有明显的多尺度特性;非均匀性梯度带,是地震可能频发地带Observation and research results show that in

5、homogeneity of medium exitsts in the interior of the earth with varying degress, the difference of inhomogeneity scale of medium revealed by seismic wave is about 8 orders of magnitude. According to the size of scatter body and seismic wavelength, the inhomogentiy of medium can be classified two typ

6、es, one is lagre scale inhomogeneity (long wavelength inhomogeneity), and other is small scale inhomogeneity (short wavelength inhomogeneity). In contemporary seismology, the determintic method used to study the large scale inhomogeneity of medium is know very well, and its method and technique have

7、 been approved by theory and practice. The small scale inhomogeneity of medium is a new research area, and its theory and method study is on starting stage. The aim of paper is to discuss 3D small scale inhomogeneity.Geological structure movement is the main cause of inhomogeneity. Studying the inho

8、mogeneity of medium in the interior of the earth, it is very important to study the producing process, force, distortion and movement stage of inhomogeneity structure boundary for knowing the strucute of earth, resource exploration, and volcano and earthquake observation and prediction.Main research

9、 contents and conclusions in the article are following.First, random medium model was described using statistical method. Model building, types and characters of ramdom medium model were discussed. The relationship between heterogeneous body and model parameters (autocorrelation length a and b, the

10、fractional velocity fluctuation) were also analysed.Second, the phenomena and the theory of S wave envelope broadening based on Von Kármán type random medium were discussed. The theory expression of power spectral density function of Von Kármán type random medium is deduced, and

11、the factors influencing duration time of S wave envelope, such as the travel distrance of Swave in random medium, the fractional velocity fluctuation of the medium and the frequency of Swave, were analyzed. Third, the relationship between the duration time of S wave envelope in multi-layer and the p

12、arameters of random medium is developed. The equivalent travel distrance is the main factors to make multi-layer random medium to single layer random medium, which set up the relation between the duration time of S wave envelope in multi-layer and the parameters of random medium, and is a base of di

13、scuss the inhomogeneity of medim by quantitive or qualitative method.Four, the forward simulation of S wave in 2D Von Kármán type random medium were modeled. The phenomena of S wave envelope broadening, the frequency of S wave, the fractional velocity fluctuation of ramdom medium and the t

14、ravel distance of S wave were analysised.Five, the 3D inhomogeneity of medium in Changbaishan Tianchi volcano were qualitatively analysised by the peak delay time of S wave envelope. The results show that the medium of Changbaishan Tianchi volcano presents strongly inhomogeneity. The inhomogeneity o

15、f medium in Changbaishan Tianchi volcano presents multi-scale character. Earthquakes usually occur around the contact band of strong and weak inhomogeneity.Six, the 3D inhomogeneity of medium in Changbaishan Tianchi volcano were quantitively analysised by the peak delay time of S wave envelope. The

16、parameters ofHurst index k and log (the main reason is the relationships between the fractional velocity fluctuation of ramdom mediumand the autocorrelation length a and b are undecoupling) were accept to describe the inhomogeneity of medium. The result also show that the medium of Changbaishan Tianchi volcano presents stron