Seismic methods are one the most commonly conducted

geophysical surveys for engineering investigations. These

methods are based upon the transmission of seismic

waves into the subsurface and recording the resulting

waveforms. The two main types of seismic surveys are

Refraction and Reflection. Seismic methods provide

engineers and geologists with the most basic of geologic

data via simple procedures with common equipment.

The seismic refraction method is based on the

measurement of the travel time of seismic waves refracted

at the interfaces between subsurface layers. Seismic

energy radiates out from a shot point, either traveling

directly through the upper layer or traveling down to

and then laterally along higher velocity layers before

returning to the surface. This energy is detected on

surface using an array of geophones spaced at regular

intervals. Beyond a certain distance from the shot point,

known as the cross-over distance, the refracted signal

is observed as a first-arrival signal at the geophones.

Observation of the travel-times of the direct and refracted

signals provides information on the depth and dip of

the refractor.

Seismic reflection profiling involves the measurement of

the two-way travel time of seismic waves transmitted

from the surface and reflected back from subsurface

features. The reflected signal is detected on surface

using an array geophones. The simplest form of seismic

reflection profiling is the constant-offset method. This

technique uses a single geophone offset from the source

by a fixed distance. The two are moved along the

survey line in equal steps with a single trace being