Detection and characterization of karstic cavesintegration of geological and geophysical techniques

Resumen

The integration of geophysical and geological methods is a sound means of studying cavities that are not accessible from the surface. In this Ph.D. Thesis, cavities under different geological, size and depth conditions were studied to establish the suitability of different techniques for void detection and characterization. The Gruta de las Maravillas cave, located within pyrite-bearing marbles in the Cerro del Castillo hill (Aracena, SW Spain), was explored through a combination of techniques: microgravity, magnetic, electrical resistivity tomography (ERT), induced polarization (IP), seismic refraction and reflection, ground penetrating radar (GPR) and geological field mapping. The geophysical anomalies obtained for the known cave were extrapolated to other parts of the hill, revealing the presence of new cavities. In addition, the sensitivity of each geophysical method for detecting caves in metallic mineralized sectors was analysed. Regarding microgravity prospection, a detailed analysis of already available regional-residual anomaly separation methods was carried out. High resolution residual gravity maps were obtained by means of first order polynomial fitting. Meanwhile, the Algaidilla cave (Estepa, Southern Spain), partially saturated with salty water and enclosed in carbonates disconnected from the surface, was studied through microgravity, ERT and IP methods. Joint interpretation made it possible to derive the approximate morphology of the cavity. Finally, a combination of microgravity and ERT techniques in 3D array were applied over the shallow gypsum caves of Sorbas (Almería, SE Spain); the measurements repeated in time-lapse allow these geophysical methods to be tested in sectors having a low contrast in physical parameters. Application of the geophysical techniques in different contexts leads to the conclusion that microgravity and ray tracing coverage in seismic refraction are, in general, the most suitable methodologies for cave detection.