In the former, resistance to flow of a seismic wave through soil is measured; in the latter, resistance of soil to movement of an electrical current is determined. Cool colors delineate shale. 5. Any mechanical vibration is initiated by a source and travels to the location where the vibration is noted. • Measurement of seismic-wave travel time is one of the most common geophysical method. There are a number of methods used to determine a site's shear wave velocity: Crosshole method; Downhole method (with a seismic CPT or a substitute device) conditions from seismic refraction data. Hot colors correspond to higher velocities, i.e., salt. Seismic refraction technique is used to determine geologic discontinuities such as fractures, cracks, faults etc., whose impact on the stability of structures can’t be overlooked. Two particular geophysical methods - seismic refraction and electrical resistivity - are most commonly used. The seismic reflection geophysical method was employed for the investigation. The seismic refraction method, due to its versatility, is one of the most commonly used geophysical methods in engineering, mining, groundwater exploration and environmental site investigations. Seismic refraction maps contrasts in seismic velocity – the speed at which seismic energy travels through soil and rock. Deep seismic reflection surveying is the most advanced technique in geophysics today, thanks to its application on a huge scale for oil and gas exploration. Geophysical site investigation methods are simple, quick and physical in nature, making them environmentally friendly and cheap. Levee failures in New Orleans in 2005 are attributable in part to poor understanding of sediments between geotechnical sites. The same field data can be used to draw different inferences. This reduces the cost involved in subsurface investigation. L.I. Seismic refraction method readily detects groundwater level when there is a change in the velocity of the same layer. Seismic refraction survey also gives the various layers in the subsurface by using the velocities of the seismic waves in the subsurface thereby helping in reducing the number of borehole that are required for the subsurface investigation at a site. In particular, in porous soils, the unsaturated vs saturated interface, is a refracting surface, efficaciously detected by the afore-mentioned exploration method (Haeni, 1988).Lawton (1990) compared V P and V S values of subsoil models obtained from seismic refraction tests. Seismic refraction provides engineers and geologists with the most basic of geologic data via simple procedures with common equipment. Seismic refraction is used when shallower depths of soil foundation are analyzed and for determining wear zones. Seismic refraction, a technique for subsurface investigation in Iowa William Praed Staub Iowa State University Follow this and additional works at:https://lib.dr.iastate.edu/rtd Part of theGeophysics and Seismology Commons This Dissertation is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. Photograph of a seismic refraction survey Seismic refraction tomogram of a salt diapir in central Utah. Electrical Resistivity Method. This method consists of the generation of elastic waves on a given point of the surface. Responses of a shock wave eminating from a source are picked up by geophone at known distance. Seismic refraction velocity-versus depth models can complement our understanding of natural soils beneath flood protection levees at locations between geotechnical sites. Seismic refraction traverses (seismic lines) are performed using an array of seismographs or geophones and an energy source.. Seismic Refraction (SR) is a surface geophysics method that utilizes the refraction of seismic waves on geology layers and rock/soil units to characterize subsurface geologic conditions. These waves are detected by receivers (vertically-sensitive geophones) placed along a linear array at the surface. Seismic Refraction Investigation of Thickness and Velocity of the Weathered Layer in Emuoha Town, Rivers State, Nigeria. (i) Seismic Refraction Method: This soil exploration method is based on the principle that sound waves travel faster in rock than in soil. Seismic reflection is a commonly accepted method for mapping subsurface stratigraphic boundaries. 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