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Geophysical Applications
Published in Stephen M. Testa, Geological Aspects of Hazardous Waste Management, 2020
Seismic techniques, whether refraction or reflection, employ a seismic wave from an acoustic source and measures the subsequent travel time of seismic waves. Subsurface features can be inferred by the analysis of the travel time of the direct and refracted waves. Sources include a sledge hammer, explosives, or other method for deeper or special applications. Geophones implanted in the ground translate seismic vibrations into an electrical signal which is then displayed on the seismograph. Seismic refraction is commonly applied to investigations of up to a few hundred feet. Resolution and depth of measurements are dependent upon spacing of the geophones. Seismic reflection is effective to depths of a few thousand feet.
A multi-disciplinary approach to active fault rupture risk characterization: 3D geological modelling of the Willunga fault, Mt Bold Dam, South Australia
Published in Jean-Pierre Tournier, Tony Bennett, Johanne Bibeau, Sustainable and Safe Dams Around the World, 2019
S.R. Macklin, Z. Terzic, J.F. Barter, P. Buchanan, M. Quigley
The seismic refraction method was the principle method adopted for shallow profiling purposes (< 50 m depth typically) and is based on the measurement of the travel time of seismic compressional waves refracted at the interfaces between different velocity subsurface layers. Eight SRT lines were surveyed across the inferred trace of the Willunga Fault. Figure 3 illustrates an example of distinct velocity changes observed when traversing across the inferred Willunga Fault at the location of SRT line 3. Subsequent trench mapping confirmed that the position and dip of the inferred Willunga Fault closely correlated with the P-wave velocity anomaly, passing through point 5 at the surface.
Site investigation and geological data collection
Published in Duncan C. Wyllie, Rock Slope Engineering, 2017
Seismic refraction – seismic surveys are used to determine the approximate location and density of layers of soil and rock, a well-defined water table, or the degree of fracturing, porosity and saturation of the rock. Seismic velocities of a variety of rock types have also been correlated with their rippability, which is a useful guideline in the selection of rock excavation methods as shown in Figure 4.4. The seismic method is effective to depths in the range of tens of metres to a maximum of a few hundred metres. Discontinuities will not be detected by seismic methods unless shear displacement has occurred and a distinct elevation change of a layer with a particular density as a result of fault movement.
Applied geophysics for cover thickness mapping in the southern Thomson Orogen
Published in Australian Journal of Earth Sciences, 2018
I. C. Roach, C. B. Folkes, J. Goodwin, J. Holzschuh, W. Jiang, A. A. McPherson, A. J. Meixner
Seismic refraction imaging of subsurface layers assumes that the seismic velocity in those layers increases with depth. A seismically slow layer below a fast layer (i.e. a velocity reversal), such as a paleoweathering profile, will be an invisible layer within refraction models, creating model depth errors (Whitely & Greenhalgh, 1979). Major velocity boundaries such as the surface weathering profile, the water-table, paleoweathering profiles and bedrock are normally distinct refraction layers that can be modelled. However, the errors introduced by slow layers are included within the seismic velocity estimations and thus depth estimations of the seismic refraction models.
Site Amplification of Iran’s Major Seismic Zones Using Attenuation Relationship
Published in Journal of Earthquake Engineering, 2018
Hamid Saffari, Yasuko Kuwata, Abbas Mahdavian
Site investigations were done using seismic refraction method by BHRC [Sinaeian et al., 2008, 2010]. The seismic refraction method is used to map geologic conditions including depth to bedrock, stratigraphy, lithology, structure, and fractures or all of these. The calculated seismic wave velocity is related to mechanical material properties. Result of refraction analysis method leads to calculation of thickness and shear velocity for upper layers and average shear wave velocity for upper 30 m (AVs30) of the site profile has been calculated by