Seismic survey
Introduction
Geophysical prospecting is a set of physical and mathematical techniques, applied to subsoil exploration for the search and study of deposits of useful substances (oil, underground water, minerals, coal, etc.), through observations made on the Earth's surface.
By applying geophysical methods it is possible to determine the stratification of soils and rocks, measuring changes in the physical characteristics of the materials, such as the speed of wave propagation, the resistivity or conductivity of the soil and/or subsoil, and the magnetic susceptibility, among others.
It consists of relating the geological structure of the subsoil through the distribution of some physical property of the subsoil; this depends on the method used.
Methods
seismic studies
They consist of artificially producing seismic waves with a small explosion or the impact on the surface of a heavy object (sometimes carried by a special truck for this task). These studies detect the presence of hydrocarbons very well. Refraction Seismic, based on the observation of the arrival times of the first ground movements at various sites, generated by a specific energy source at a given site. The data set obtained in the data acquisition consists of time versus distance records. These series are interpreted in terms of the depth to interfaces between soil layers and the propagation speeds of the P (or S) wave in each layer. These speeds are controlled by the elastic parameters that describe the material. In Reflection Seismic the analysis is based on the energy of the vibrations after the ground movement has started. Specifically, the study focuses on the ground movements induced by the reflection of waves, in the different interfaces of layers, which have been generated at a specific site. In reflection, information is extracted from the subsoil by studying the amplitude and shape of the ground movements. For this reason, seismic methods are used to measure the speed of wave propagation in the subsoil, allowing the subsoil to be characterized from the surface to hundreds of meters. Uses: Characterization of the rock basement, determination of the stratigraphy and geometry of the subsoil, support in the detection of groundwater, evaluation of material banks.