Procedure

The detectors are generally placed at varying distance from the shot point but along the straight line. The arrival time of the first impulse at each geophone is utilized. If the successfully deeper strata transmit the waves with increasingly greater velocities, the path traveled by the first impulse will be similar to those shown in fig. 1.7. Those recorded by the nearest recorders pass entirely through the overburden, whereas those first reaching the farther detectors travel downward through the lower- velocity material, horizontally within the higher velocity stratum, and return to the surface as shown in the fig. 1.7. By plotting the travel times

( and ) as a function of the distances between the geophones and the shot points ( and ) as shown in fig. 1.8, a curve is obtained which indicates the wave velocity in each stratum and which may be used to determine the depths to the boundaries between the strata.

Where,
and are the depths of the strata,
,
,
Sin
Sin