Seismic
Seismic prospecting is a method to visualize the geological structures at depth by analyzing the echoes of seismic waves. It should not be confused with seismology , which is the study of seismic waves and earthquakes for themselves.
Studied seismic waves can be natural ( earthquakes ) or artificial (vibrating truck, explosive, air gun, etc.). In all cases, they follow the same laws as light waves. The two major seismic techniques are:
- seismic reflection;
- seismic refraction.
Summary |
The seismic reflection
The seismic reflection uses reflected waves on interfaces between different levels geological. Guns are used compressed air to sea, truck vibrators or dynamite to earth to create waves. The emitted waves propagate and are partially reflected at each boundary layer. They are received by sensors ( hydrophones at sea or on land geophones). The single-channel seismic reflection can be or multichannel. In the latter case, in addition to increasing the signal to noise ratio, it is possible to calculate the velocities of the media traversed. This information is then used to convert the data in depth.
The seismic refraction
The seismic refraction using wave propagation along the interfaces between geological levels. This method is particularly suitable for certain applications of civil engineering and hydrology. She estimates the velocity model and the dip of the layers. She is currently limited in practice targets with depths less than 300m, but is originally from the discovery in 1956 of oil field of Hassi Messaoud , the largest in Africa, a average depth of 3300 meters.
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