The lower panel shows wave propagation in the 1-D layered P-wave velocity model of the Campi Flegrei volcanic caldera, southern Italy (see Zollo et al. 2008, Geophys. Res. Lett.), and the upper panel shows the corresponding seismogram section.
The wave propagation was computed with the acoustic 2-D finite-difference code SUFDMOD2 from CWP/SU Seismic Unix, and the individual frames were generated with the Generic Mapping Tools (GMT).