|
The boundary element-image method is proposed as a method for generating synthetic seismograms in a system of piecewise homogeneous layers. In contrast with many other methods (such as finite difference) in which the boundary conditions are represented simply by a change of material properties, the present approach uses the boundary conditions explicitly in order to develop a system of integral equations. As in the indirect boundary element method, the scattered seismic waves are presumed to result from the action of ficitious sources. However, as in the image method, these fictitious sources are located outside of the domain through which the scattered waves progate. This combination of the image and boundary element methods thereby avoids introducing additional singularities (in the form of ficitious sources) into the wave equation for the scattered waves. Although this method can be formulated in a general way, specific computational advantages occur when the basis and testing functions are chosen as harmonically related complex sinusoids. Physically, this corresponds to a plane wave expansion of the scattered waves. Computationally, when considering piecewise linear interfaces, this results in a (possibly) large system of simultaneous algebraic equations having matrix elements which can be calculated analytically. This method is applied to the reflection of seismic-waves from a V-shaped reflector subjected to two different incident waves: a plane wave and a cyclindrical wave created by a line source. The synthetic seismograms for both cases are presented (in the form of time sections) and then processed in an attempt to reconstruct the geometry of the reflector (in the form of a depth section). ¿ American Geophysical Union 1990 |