【摘要】 我们发展了一种模拟复杂地表下含裂缝介质地震波场的方法,这对于解释山地地区的地震资料具有重要意义。基于Coates-Schoenberg方法,把裂缝引入到有限差分法(FD)中,从而使包含裂缝的单元里的弹性介质就具有了局部的各向异性。为了模拟起伏的地表地形,我们借助于贴体网格,将笛卡尔坐标系的具有水平对称轴的横向各向同性介质(HTI)的弹性波方程和自由边界条件变换到曲线坐标系中,采用一种稳定的、显式的二阶精度的有限差分方法离散(曲线坐标系)HTI介质中的弹性波方程。数值实例充分地展现了在不规则地球表面的影响下裂缝介质中地震波传播的复杂性。合成地震记录和波场快照表明裂缝端点产生的散射波在地表处会受不规则地表地形的作用,再次被散射;同理,地表地形产生的散射波,经过裂缝端点时也会被再次散射,尤其是瑞利面波产生的散射波,因其能量很强,严重污染了地震记录,使得识别地下裂缝等产生的有效信息变得异常困难。这对山地地震勘探中资料的解释具有重要意义。更多还原

【Abstract】 We present a finite difference(FD) method for the simulation of seismic wave fields in fractured medium with an irregular(non-flat) free surface which is beneficial for interpreting exploration data acquired in mountainous regions.Fractures are introduced through the Coates-Schoenberg approach into the FD scheme which leads to local anisotropic properties of the media where fractures are embedded.To implement surface topography,we take advantage of the boundary-conforming grid and map a rectangular grid onto a curved one.We use a stable and explicit second-order accurate finite difference scheme to discretize the elastic wave equations(in a curvilinear coordinate system) in a 2D heterogeneous transversely isotropic medium with a horizontal axis of symmetry(HTI).Efficiency tests performed by different numerical experiments clearly illustrate the influence of an irregular free surface on seismic wave propagation in fractured media which may be significant to mountain seismic exploration.The tests also illustrate that the scattered waves induced by the tips of the fracture are re-scattered by the features of the free surface topography.The scattered waves provoked by the topography are re-scattered by the fractures,especially Rayleigh wave scattering whose amplitudes are much larger than others and making it very difficult to identify effective information from the fractures.更多还原