Fig. 5.

Example of the waveforms recorded on PZT receivers at a$\theta$ = 0${}^{\circ }$, b $\theta$ = 12.2${}^{\circ }$, and c $\theta$ = 26.2${}^{\circ }$, for the impulsive (left panels) and step-like source (right panels). Signals were recorded at 20 dB gain. The waveforms are the result of stacking and averaging 50 traces (black line). Using the generalized ray theory [16], the true Green’s functions are given along with the theoretical wave arrivals including reflections (blue line). The purple regions in a emphasize the cross-talk from the HVP in the system at the lowest source–receiver distance