Inema Ingenieros Asesores S.L., aims to offer an alternative that permits a better characterisation of the subsurface, obtain a better generic idea of the area, minimising the number of boreholes and concentrating them on areas that geophysics has dictated as of major interest, depending on the objectives of the study.

The majority of the geophysical methods are non-intrusive, capable of covering great areas of land in a short time, extracting at the same time a large volume of information.

 

1. SEISMIC METHODS REFRACTION/ REFLECTION ON LAND AND MARINE

These methods are based on analysis of the distribution of seismic velocities originating from an artificial source (blows or explosions above the ground surface). The seismic velocity increases in materials with a greater density, permitting the distinction between distinct types of materials.

The most important applications are:

•Delimitation and volume estimation of landfill

•Definition of fill

•Detection of cavities

•Testing of ability to excavate the ground (rippability)

•Slope stability determination

•Subsurface stratigraphy

•Location of water table

•Mapping of geological structure

•Cost prediction of works

•Pile testing.

•Evaluation of exploitable deposits

 

2. ELECTRICAL METHODS (VERTICAL ELECTRIC SOUNDING, LAND BASED AND AQUATIC ELECTRICAL IMAGING SURVEYS)

Electrical methods are the oldest of the geophysical techniques and are used by geologists, geophysicists and engineers to distinguish and characterize the subsurface.

All the materials in the earth give a resistance to the flow of current. This property is called geo-electrical resistivity, and permits us to differentiate between these materials.

Its most important applications are:

•Detection of contaminant plumes

•Delimitation of landfill sites

•Detection and volume determination of leachates

•Cavity detection

•Geo-electric resistivity of the subsurface

•Telluric currents

•Subsurface stratigraphy

•Location of water table

•Detection of geological structures

•Coastal works

•Dams

•Evaluation of reserves of arid sands, gravels, etc.

•Evaluation of exploitable deposits

 

3. GRAVIMETRY

The principal objective of gravimetry is to measure the anomalies in the gravity field of the earth caused by changes in density between distinct materials. The field data must be corrected with respect to points of reference of known gravity. The corrections are made with respect to time, topographic altitude, geographic position, movements and proximity to large masses of rock.

The most important applications are:

•Delimitation and determination of volume of solid urban residues

•Characterisation of areas of residues or spill

•Detection of cavities

•Stratigraphy of terrain

•Location of metallic and non-metallic mineral deposits

 

4. MAGNETIC/ ELECTROMAGNETIC METHODS

The magnetic field of the earth is measured with an apparatus called a magnetometer. This instrument measures variations in the magnetic field of the earth, provoked locally by ferric objects.

The electromagnetic field is provoked using a transmitter antenna and measured by separate receiver antenna. The antenna transmits an alternating current creating a primary electromagnetic field. If this field is situated above a good conductor, this creates a secondary magnetic field. The receiver antenna detects the magnetic field using this we can estimate the geoelectrical conductivity at the point of measurement.

The most important applications are:

•Delimitation and calculation of volume of land fill

•Detection of metallic deposits that can generate sources

•Detection of cavities

•Location of contaminant plumes

•Detection of geologic structure

•Cable detection

•Detection of metal tubes

•Metal detection

•Evaluation of mineral deposits

 

5. NUCLEAR MAGNETIC RESONANCE FOR EXPLORATION OF GROUNDWATERS.

Nuclear magnetic resonance is based on the tendency of hydrogen protons to produce a magnetic field when exited by a static magnetic field.

The great majority of the hydrogen atoms found in the subsurface form part of water molecules. This method gives a direct estimate of water content of rocks, and has been used in borehole petroleum geophysics for some time. As a surface geophysics method it is relatively new.