A boundary element (be) method is developed to calculate the two-dimensional P-SV elastic response for crustal wave guides with irregular topographic features. To simulate long-range propagation of regional waves, a connection technique is proposed to avoid large matrix inversions that become formidable for long-range, high-frequency problems. By using this technique, a long crustal wave guide can be divided into relatively shorter sections, and the be method can be used section by section to model the effects of rough topography on wave propagation at extended regional distances. The validity of the technique is tested by comparison with a direct calculation. Numerical simulations with this scheme show that rough topography can scatter the P and Rayleigh waves and attenuate the energy propagating in the wave guide. This method can be used in computing the site effects on sites such as canyons, mountains, and valleys. The connection technique expands this method to deal with large earth models with irregular topography.