Figure 1 (from Fowler p 120 The configuration for the 110N 36 channel active source refraction survey: Long survey: Source is at x=0, geophone #1 is at 1m, #36 is at 28m Short survey: Source is at x=0, geophone #1 is at 0.3889m, #36 is at 14m Record sections 1+3 Ground roll (Rayleigh wave) slope 1/(0.92*ß_1) 18m 18m X_cross is this distance at which the direct wave and the refracted wave arrive at the same time. X_c is the distance where you will start seeing head waves arriving. At this distance the head wave has a segment AB that has zero length (so it is a reflected wave with incidence angle i_critical). ß1 is the shear wave velocity for the upper layer. The Rayleigh wave takes a ray path SR in the upper layer.

Distance from source (m) Which way is up? Time after shot (ms) 0.5 Distance from source (m) 18 milliseconds New Record Section 1: Shooting North, source 0.5 m from first geophone, 0.5 m spacing between geophones

Distance from source (m) Which way is up? Time after shot (ms) 18 Distance from source (m) 0.5 milliseconds New Record Section 2: Shooting South, source 0.5 m from first geophone, 0.5 m spacing between geophones

Distance from source (m) Which way is up? Time after shot (ms) 0.3889 Distance from source (m) 14 milliseconds Record Section 3: Shooting South, source 0.3889 m from first geophone, 0.3889 m spacing between geophones