Onshore Seismic Refraction

Generalities

The seismic refraction is a non-destructive tool to interpret the properties of the soil, and to determine the depth of the bedrock by analysing the P wave velocities variations of seismic waves transmitted (waves of shock).

The principle of this is to measure the arrival times of the compression waves (P wave) produced by a controlled seismic source (weight drop, airgun, sledgehammer, explosive,…) as a function of the distance. The most hard soil layers have high speeds (rock) compared to loose media (alluvium) with lower speeds.

The refraction seismic measurements are carried out along longitudinal profiles made up of several aligned geophones, with different impacts positioned along the profile. The recording of seismic data is carried out on Geometrics recorders (www.geometrics.com) and controlled by MGOS software.

The time plotting of the first arrivals of P seismic waves is performed with Geogiga software (www.geogiga.com). The results, corresponding to the velocities propagation of the compression wave, in the form of tables or synthetic sections, make it possible to highlight areas of contrast between soils with different degree of alterations.

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  Dromochronic