Waveguides formed between the earth's free-surface and sharp subsurface
velocity discontinuities, such as the watertable, may have a significant
impact on high-resolution seismic refraction and reflection data.
Energy trapped in such waveguides may propagate over long distances
with little loss due to geometrical spreading. The dispersive nature
of the guided waves results in pronounced shingling of the first
arrivals. This narrows the ''optimum reflection window'' between
the first arrivals and the ground roll, and may lead to mispicking
of first breaks and difficulties in identifying and processing shallow
reflections.