Synthetic model (two layers, velocity within each layer is constant)

This synthetic model is essentially composed of two constant velocity layers with a transient zone between the two layers. The geometrical size of this model is the same as last one. The velocity of upper layer is 2000m/s and that of lower one 3000m/s. The interface will make the Runge-Kutta algorithm fail if the model is not smoothed reasonably. We apply a triangle smoothing filter to the model along x, y, z axis. The result is shown in Figure 4.

 

model2-smooth
Figure 4 Left: The sharp interface makes the Runge-Kutta algorithm fail. The rays propagate in random directions when passing through the interface. Some of them are even reflected back to the upper layer. Right: The interface has been smoothed by the triangle smoothing filter. The rays' propagating directions follow Snell's law. All the rays pass through the transition zone and enter the lower layer.