I ran a 60 m seismic line. Energization with hammer. 12 (10 hz vertical 5 m spaced) geophones and 5 shots (15 m spaced). Record length 0.5 s. Thanks to a borehole near a estrata of gravelly silt man-made (0.40 m) and very soft silty clay (to 5 m) and then clay improves its consistency deeper. My seismic traces seemed to be ok, but at office the principal wave train gives 200 m/s and first arrivals refractions are that weak that can not be easily identified. I think the principal train wave shadows them.
My question: ¿What is the meaning of a 200 m/s train wave in geophysics?