oa Seismic Surveying For The Non-Geophysicist

Seismic surveying is a geophysical technique that employs sound<br>waves to image subsurface structures. In suitable environments, seismic<br>methods yield useful data on bedrock topography, soil layering, aquifers<br>and aquitards, faulting, buried channels and lateral changes in rock and soil.<br>Acoustic energy is introduced into the ground by means of an<br>impact, explosion or vibratory source. Diverse types of waves result in<br>differing modes of vibration and velocities. Measurement of transit<br>times and apparent velocities of some of these waves yield data on<br>subsurface properties. Refraction surveying uses the patterns of first<br>arrival of waves to determine depth and velocity of the interfaces.<br>Reflection surveying measures energy arriving later in the seismogram<br>that has been echoed from interfaces with contrasting acoustical<br>properties. And boreholes are often employed to measure sound waves<br>introduced either at the surface or in another borehole. All techniques<br>have pitfalls and limitations that should be understood and accounted for<br>when interpreting the data.<br>Inexpensive personal computers, advances in acquisition<br>instrumentation and processing software have made seismic surveying<br>less costly, less time consuming and more effective. In conjunction with<br>ground truth from geophysical techniques or limited drilling, seismic<br>surveying can reduce contaminant cleanup costs, assist road construction<br>and help find water. These times and cost savings make seismic<br>surveying a sensible tool for problems in hydrogeology, construction, waste management and resource exploration.