In practice, however, an approach of multiple (for example, four) 2-D profiling in different directions at different places within the same site has been usually taken to maximize the thoroughness of the characterization for a given deployment of field equipment and crews (Fig. 1). This approach makes it possible to evaluate the stiffness information in a regional, as well as local, scale. A pseudo 3-D map of bedrock topography is constructed at this stage, based on the arbitrary high value of Vs immediately following the top soil layer mapped (Fig. 2). In addition, this approach enables detection of shallow voids and cavities (for example, 10 m or less)—the most dangerous potential hazards—through a special processing approach called side scattering analysis (SSA) described below. Recently, a 3-D processing has been applied to generate a cubic grid Vs data set by using multiple sets of 2-D Vs data. More details are explained below.
