Seismic refraction profiles the subsurface
by determining the path and velocity of
compressional or shear waves. The waves are
created by shot, hammer, weight drop, or some
comparable method to put energy into the
ground.
Detectors are laid
out at regular intervals in a line to measure the
first arrival energy and the time of arrival.
The data are plotted
in time distance graphs, from which velocity of
and depth to layers can be calculated. This is
possible because the compression or shear waves
are refracted across layer boundaries where there
is a difference in elastic and density
properties.
Shots are normally reversed
from one end of the line to the other to determine
whether or not the layering is horizontal or
dipping.
