Geophysics is an ensemble of techniques and procedures to obtain information from the underground, without drilling it. In general, an image of the kind we would get if we were inside IS NOT obtained. A descriptive and interpretable image is truly achieved, but requires a complex procedure and is somewhat a little bit less miraculous.
The data are physical quantities observed in the field by the use of geophysical instruments. Directly or after some processing, maps are produced from them showing information about the subsurface. A quantitative final interpretation directly based on these maps would be incomplete or misleading. Another step is needed.
Each geophysical method reacts, mainly, to a single physical property of the terrain (density, resistivity, etc.). What ideally is sought is their spatial distribution in the subsurface or/and the temporal evolution. The systematic procedure that obtains this spatial distribution of parameters from the observed data is called Inversion. Inversion is, in general, mathematically complex. But some efficient algorithms have been incorporated in free and commercial codes of popular use.
The result of the inversion is an image of physical properties. This estimation relies on the choice of certain numerical parameters in the code. Therefore, some sensible knowledge of the mathematical structure is highly desirable (the default option is also an option, even if it remains hidden to the user perception).
More than one final image is possible, honoring the observations. If some images are reasonable, possibly the shared structure has to be extracted and taken into account. Some proposals, however, would be dispensable in light of the data. Here, then, the joint work of specialists from different fields is very important to achieve a reasonable, consistent and maybe correct interpretation.
Our team Works with the following geophysical techniques:
- Gravity: sensitive to the density of the materials. We have a digital gravity meter Scintrex CG-5.
- Magnetics: Sensitive to the magnetic susceptibility of the materials. We have a proton precession magnetometer/gradiometer G-856AXfrom GEOMETRICS.
- Radar: Sensitive to the dielectric constant. We have available a quite complete family of shielded antennae (100, 250, 500 and 800 MHz) as well as non shielded at 100 MHz from MALA GEOSCIENCE.
- Time domain Electromagnetics (TDEM): Sensitive to the conductivity of the materials. A MONEX GEOSCOPE unit is available able to measure the 3D magnetic field produced both at very shallow depths (less than three meters) and at more than 1 km.
- Sensitive to the resistivity of the materials: An AGI tomography instrument is available both for 2D and 3D surveys.
The team uses specialized software for processing/inversión/interpretaion: OASIS MONTAJ; GRAVAP; EARTHIMAGER 2D/3D; COMSOL or programs the required code.
Information about the projects carried over in this line can be seen in the Projects submenu.
- Detailed gravity surveys have been performed to locate cavities associated with mining activities and docks in harbors. Also the gravity anomaly produced by a CO2plume injected in a coal seam has been researched.
- The magnetic method has been employed to characterize the distribution of minerals in clogged dams. The techniques is nowadays being used in archaeology and forensic collaborations.
- Radar has been employed in forensic applications such as mass graves or individual burials and in archaeological collaborations dealing with the location of middle age churches or remains of villages in different places throughout Spain.