【作者】 吴如山；

【Author】 Wu Rushan~①(Earth Resources Laboratory Department of Earth,Atmospheric and Planetary Sciences MIT,Cambridge,USA)

【机构】 美国麻省理工学院地球、大气及行星科学系； 中国科学院地球物理研究所；

【摘要】 本文建议用三种方法由地震数据去估计岩石圈的非均谱（非均匀体的功率谱）:1)利用尾波激发谱的后向散射测量;2)利用S波及尾波的散射衰减测量;3)利用P波横跨大型地震台阵的透射起伏测量。基于过去对地震波散射的观测,岩石圈三维非均匀体（考虑为各向同性时）可被模型化为分数布郎空间对线函数,其缩尺幂数（即Hurst数）H=1/2～1/3。这样的分数布郎函数是一个自仿形（Fractal）,且具有自仿维数D₃=4-H=7/2～11/3。相应的一维功率谱是一个具有等乘幂律的谱,其幂数p=-（2H+1）=-2～-5/3。地表面和三维非均匀体等强面的交线具有自仿维数D₁=3/2～5/3。如果我们假设断层面是沿着三维非均匀体的等强面发展且被断裂动力过程所平滑,D₁就给出了地表断层迹线自仿维数的上限。最近沿圣安德烈斯断层测得的自仿维数的某些结果也在文中进行了讨论。更多还原

【Abstract】 Three methods are suggested to estimate the inhomogeneity spectrum of the lithosphere from seismic data:1) a backscattering measurement from coda excitation spectra,2) a scattering attenuation measurement from S and coda waves,3) a transmission fluctuation measurement from P waves across a large seismic array.Based on past observations of seismic wave scattering,the 3-D inhomogeneities in the lithosphere（when considered as isotropic） can be modeled as a fractional Brownian space-to-line function with the scaling exponent （Hurst number） H=1/2～1/3.which is a fractal with the fractal dimension D₃=4-H= 7/ 2～11/3.The corresponding 1-D power spectrum is a power law spectrum with the power p=-（2H+1） =-2～-5/3.The intersect line between the Earth’s surface and the isosurface of the 3-D inhomogeneities has a fractal dimension D₁= 3/2～5/3.This sets an upper limit for the fractal dimension of fault traces on the surface if we assume that the fault surfaces are developed along the isosurfaces of the 3-D inhomogeneities and smoothed by the rupture dynamics.Some recent measurements of fractal dimension along the San Andreas fault are discussed.更多还原