用散射體波隨機反演研究長白山火山區(qū)介質(zhì)非均勻性

1、用散射體波隨機反演研究長白山火山區(qū)介質(zhì)非均勻性        觀測和研究表明,地球內(nèi)部存在著不同程度的介質(zhì)非均勻性,由地震波所揭示的介質(zhì)非均勻尺度可達8個數(shù)量級。根據(jù)散射體與地震波長之間的大小關(guān)系,將地球內(nèi)部介質(zhì)非均勻性分為兩類:即大尺度非均勻性(長波長非均勻性)和小尺度非均勻性(短波長非均勻性)。在當(dāng)代地震學(xué)中,用確定性方法研究大尺度非均勻性已是眾所共知的事情,目前技術(shù)方法也已比較成熟；對小尺度非均勻性的研究則是一個全新的研究領(lǐng)域,其理論探索和方法研究還處于起步階段,本文重點對3D小尺度介質(zhì)非均勻性進行了研究。介

2、質(zhì)非均勻性往往是地質(zhì)構(gòu)造運動的產(chǎn)物。研究地球內(nèi)部介質(zhì)的非均勻性,對于了解地球內(nèi)部非均勻結(jié)構(gòu),特別是非均勻結(jié)構(gòu)邊界的產(chǎn)生過程、受力、變形及運動狀態(tài)等對研究地球動力學(xué)、資源勘探、火山、地震觀測預(yù)報均有重要的意義。論文主要研究內(nèi)容及結(jié)論如下:1.利用統(tǒng)計學(xué)方法對隨機介質(zhì)模型進行了論述。論述了隨機介質(zhì)模型的建立方法、隨機介質(zhì)模型的類型及其特點;探討了描述隨機介質(zhì)模型的兩個主要參數(shù)(模型相關(guān)長度a、b和擾動標(biāo)準(zhǔn)差)和隨機介質(zhì)中的非均勻體之間的關(guān)系進行了討論。2.論述了Von Karman型隨機介質(zhì)中S波包絡(luò)展寬理論?；陔p曲拋物線近似法研究了Von Karman型隨機介質(zhì)中S波包絡(luò)展寬現(xiàn)象;探討了Von

3、 Karman型隨機介質(zhì)非均勻性能量譜估計方法:分析了S波傳播距離、激發(fā)源頻率等對S波包絡(luò)展寬的影響。3.論述了多層非均勻介質(zhì)(非均衡隨機介質(zhì))S波包絡(luò)延時與隨機介質(zhì)模型參數(shù)之間的關(guān)系。通過等效傳播長度將多層隨機介質(zhì)(各層具有不同的速度擾動率)轉(zhuǎn)換為等效單層隨機介質(zhì)模型,建立了S波包絡(luò)延時與隨機介質(zhì)模型參數(shù)之間的關(guān)系,為定量或定性描述介質(zhì)非均勻性奠定了基礎(chǔ)。4.采用有限差分法對二維Von Karman型隨機介質(zhì)中S波波場進行正演模擬,分析Von Karman型隨機介質(zhì)中S波包絡(luò)線展寬現(xiàn)象,探討了激發(fā)源的頻率、介質(zhì)速度擾動率及波傳播的距離對S波包絡(luò)線展寬的影響。5.采用S波包絡(luò)峰值延時定性研究了

4、長白山天池火山區(qū)3D介質(zhì)非均勻性。研究結(jié)果表明:長白山天池火山口地區(qū)地殼介質(zhì)呈現(xiàn)強烈的橫向和縱向非均勻性;天池火山口地區(qū)介質(zhì)非均勻性具有多尺度特性或頻率特性;介質(zhì)非均勻性梯度帶,是地震頻發(fā)地帶。6.采用S波包絡(luò)延時定量研究了長白山天池火山區(qū)3D介質(zhì)非均勻性。用Hurst指數(shù)k和log(?)(因模型速度擾動率和模型特征尺度相關(guān)距離a并不解耦)對介質(zhì)非均勻性進行了定量描述。研究結(jié)果表明:天池火山口地區(qū)地殼介質(zhì)呈現(xiàn)強烈的非均勻性;天池火山口地區(qū)介質(zhì)非均勻性具有明顯的多尺度特性;非均勻性梯度帶,是地震可能頻發(fā)地帶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