The exploration of a sub-surface geology by means of seismic waves, which are generated artificially and have greater penetrating characteristics than GPR. Seismic reflection profiling involves the measurement of the two-way travel time of seismic waves transmitted from surface and reflected back to the surface at the interfaces between contrasting geological layers. Reflection of the transmitted energy will only occur when there is a contrast in the acoustic impedance (product of the seismic velocity and density) between these layers. The strength of the contrast in the acoustic impedance of the two layers determines the amplitude of the reflected signal. The reflected signal is detected on surface using an array of high frequency geophones. Seismic energy is provided by a ‘shot’ on surface. For shallow seismics this will normally comprise a hammer and plate, weight drop or explosive charge. We normally use seismic reflection and seismic refraction to map deeper elements of the subsurface or to correlate with GPR measurements. Analysis of seismic methods can give “engineer-related” information about the elastic properties of materials, such density and porosity. SSR also can detect geologic structures in fault zones, find shallow, soft layers of underground earth materials, reduce mapping uncertainties and can greatly reduce the investigation costs of engineering projects. Seismic Reflection is used to determine:
Seismic Reflection is used to determine:
- Bedrock quality, profile, and depth
- Degree of alteration and thickness of overburden
- Detection and evaluation of fault zones in tectonically active areas
- Fractured and faulted areas
- Water table level and continuity
- Elastic moduli values for soils and bedrock