Effects of surface and subsurface irregularities on the amplitudes of monochromatic waves

Abstract

Measurements of surface ground motion generated by forced vibration of a nine-story reinforced concrete building at a distance of 2 to 5.5 km are described. Three components of the displacement field were measured at 13 points along a line traversing an elongated canyon underlain by a shallow and dipping alluvial layer. The variations of measured displacement amplitudes have been modeled by (a) a two dimensional surface topographic feature corresponding to the average cross section of the canyon and (b) by a two-dimensional model of an alluvium valley excited by a line source. Comparison of the observed and computed amplitude variations with distance suggests that for the geometry corresponding to this experiment the effect of the dipping layer of alluvium seems to play a considerably more important role than the canyon.