自相似型各向异性自组织介质中地震波场动力学响应  

Seismic sounding of anisotropic self-similar self-organized medium

作　　者：刘永霞[1] 徐涛[1] 赵兵[1] 刘春成[1,2] 

机构地区：[1]岩石圈演化国家重点实验室中国科学院地质与地球物理研究所,北京100029 [2]中国海洋石油天津分公司,天津300452

出　　处：《地球物理学报》2007年第1期221-232,共12页Chinese Journal of Geophysics

基　　金：国家自然科学基金项目(40234044;40374010;40404009);科技部973项目(2002CB412604)资助

摘　　要：地下岩石结构/构造和矿物组成在小尺度上存在的不均匀性和各向异性会导致地震波速度的分形分布,进而衍生出自组织介质模型.本文针对地球内部岩浆垂向侵入及横向溢流为特征的岩浆作用,开展自相似型各向异性自组织介质的地震波动力学响应研究.基于二维自组织介质模型和声波方程,本文利用有限差分法模拟了不同强度岩浆侵入和溢流作用形成的自组织介质中地震波场,并进行了波场特征分析.研究结果表明:(1)在横向溢流作用为主的自组织介质中,横向相关长度小于地震波波长的条件下,聚焦效应随着横向相关长度的增大而增强,地震波能量随之增强;反之,在横向相关长度大于地震波波长的条件下,散射效应随横向相关长度的增大而增强,地震波能量随之减弱.(2)在垂向侵入作用为主的自组织介质中,随着垂向相关长度增大,散射效应增强,地震波的能量也随之迅速减弱.(3)岩浆作用的自组织强度增强,地震波的能量增大,而中心频率无变化.(4)自组织介质具有相同的小尺度扰动,其速度梯度背景越小,地震波能量在炮点附近越集中.(5)当多层自组织介质共存,特征层位的波场特征仍以各自的自组织特性为主,因此利用实际资料中不同层位的地震反射特征可推测地下介质的自组织性质.The multi-scale variation in composition and anisotropy in rocks and minerals may cause corresponding fractal variations of seismic velocity hence lead to self-organized models. Based on 2-D selforganized models with three layers and the acoustic finite difference method, we investigate the seismic sounding in the anisotropic self-similar medium to explain the volcano vertical or transverse intrusion in the earth. We find some interesting phenomena. In the horizontal intrusion medium, the diffraction and refraction of waves at randomly distributed inhomogeneities results in a random focusing and defocusing of wave energy and consequently results in an increase of the amplitude fluctuation with increasing propagation distances. When the lateral correlation length increases within the wavelength, focusing of energy will be enhanced. While it continues to increase beyond the wavelength, defocusing will play a main role and wave energy decreases greatly. In the self-similar media dominated by vertical intrusion, diffraction of seismic waves becomes noticeable. Moreover, the random amplitudes fortify the reflection energy and the large-scale velocity backgrounds influence the assembling of waves. We also investigated two-layer random medium like the crust, the result shows that seismic recordings from different layers carry self-organized characteristics of corresponding layer. Therefore, we can detect the characteristics of the earth in the field data.

关 键 词：二维自组织模型 各向异性 横向溢流 垂向侵入 

分 类 号：P315[天文地球—地震学]