Figure 2. VSP data acquired in a well that was drilled through the basalt layer and into the interval where the hydrocarbon play was focused. All data are recorded below the surface basalt layer. These data confirm that the downgoing wavefield illuminates deep targets, and that robust upgoing reflections are created. The diagram on the right shows the orientations of the particle-displacement vectors (short arrows) associated with downgoing and upgoing raypaths. The large arrows atop the data panels identify downgoing and upgoing P and S events.