The method can also use not only surface data, but also borehole data for imaging the vertical structures and thin high velocity layers. In this paper, we firstly describe the detail of the analysis method and demonstrate its performance through some numerical examples. Finally we show two actual examples of application of this new method to civil engineering investigations. Figure 1 shows the processing flow used in the method. The model is divided into many thin layers, and the width of each cell is chosen as the receiver interval.
Every cell has an identical velocity value.
During the iterations, the velocity of each cell is updated under the constraint that velocity increases with depth. In this algorithm, we can use traveltimes of seismic waves generated or received within boreholes together with those for the surface sources and receivers. In civil engineering applications, subsurface velocity model is often described by a layered model, in which each layer has a constant velocity. Because, it is useful for civil engineering design works to classify the underground area of interest as simply as possible, at least in the beginning stage of the site investigation. There are also often some sites which have clear boundaries of rock quality.