Additional Information
Applications
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Seismic Reflection
The seismic reflection method is an efficient and cost effective means of gathering huge volumes of data regarding the engineering properties of rocks, such as Bulk Modulus, Young's Modulus, Shear Modulus, and Poisson's ratio - the elastic constants of a rock. The density of rocks can be estimated directly from seismic velocity information. Shallow faults, isolated sand lenses or cavity features, aquifer zones, and other shallow earth structures can also be identified with seismic reflection.
 The seismic reflection method is the measurement of seismic waves transmitted from the surface and reflected back to the surface at the interfaces between contrasting geological layers. The layers reflect the energy due to the acoustic impedance between these layers - a product of the seismic velocity and density. The stronger the contrast in the acoustic impedance of the two layers, the greater the amplitude of the reflected signal. The reflected energy is detected at the surface using an array of high frequency geophones and then digitally recorded on a seismograph. The source of energy is typically a hammer and plate, weight drop or explosive charge. The source spacing or interval is designed to obtain reflections from the same point on the interface at different geophones in the array or common mid-point (CMP) collection. A reflection profile is produced from measurements of the two-way travel times at each geophone.
Typical applications of the Seismic Reflection method:
- Bulk, shear, and Young’s Moduli, and Poisson’s ratio
- determine rock density
- 2D and 3D statigraphic mapping/modeling
- determine depth to water table
- determine depth to bedrock
- locate fractures zones in bedrock
- contour mapping of bedrock
- estimate earth rippability
- image voids, caverns, sinkholes, washouts
- measure thickness of aggregate deposits
- determine depth of landfills
- determine thickness of overburden
- map topography of groundwater
Seismic Reflection Tomograph
Reflection tomography (P-Wave and S-Wave) is used to delineate stratigraphy, identify fracture zones in bedrock (low velocity zones), and provide velocity profile for rippability study. The example section below represents a P-Wave reflection tomography section showing velocity contrasts indicating variations in soil density, moisture content, etc. Soil modulus data are extracted from formulas to present an actual image of the vertical and horizontal variations in geologic elastic properties
Two-dimensional P and S wave tomography profiles showing site geologic structure and stratigraphy across 240 ft seismic line. The tomography sections represent the horizontal and vertical distribution of P and S wave velocity.
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