Ó. Pueyo Anchuela

Characterization of the Karstic Process in an Urban Environment Using GPR Surveys

In this work the authors present an analysis of the applicability of ground penetrating radar (GPR) to karstic hazard evaluation in urban areas by means of several case studies. The main objective is to characterize the origin of pathologies in buildings and other facilities, and of subsidence processes, and to identify their causative phenomena in the subsoil. This study involves the analysis of resolution, penetration characteristics and noise affecting GPR signals in urban areas. The analyzed case studies are located in the Central Ebro Basin (NE Spain), where the main hazards are related to mantled karst (solution of evaporites below alluvial deposits). The studied examples show that in areas affected by karst activity with medium to high subsidence rates, interpretation of GPR profiles allows defining collapses, subsidence, surficial repairs (either historical or recent) and underground cavities.

Magnetometry and ground-penetrating radar surveys applied to tracing potential collectors of mining-derived pollutants in coastal sediments (Piscinas Bay, Montevecchio mining area, SW Sardinia)

Abstract Dispersion of pollutants from mining areas can result in risks to human health. The dynamic interaction of geological processes can generate complex situations that favor enrichment in toxic elements by sedimentary and diagenetic mechanisms. In order to explore the distribution of iron-rich minerals in coastal and river sediments, a geophysical campaign was performed along the outlet of the Piscinas and Naracauli Rivers that drain two abandoned mining areas in SW Sardinia. Both rivers flow into the Mediterranean Sea, a bay where fluvial, marine, and eolian processes interact. The geophysical campaign comprised magnetometry and ground-penetrating radar surveys. Magnetic properties were controlled by means of magnetic susceptibility measurements along the beach and dune areas, through sampling of surface sediments, natural outcrops and trenches, and considering different grain size intervals. Results indicate enrichment in ferromagnetic minerals at the leeside of dunes and berms. Sedimentological interpretation is supported by means of ground-penetrating radar. Due to both sedimentary and diagenetic processes, the 100- to 300-μm fraction of fine sands exhibits high susceptibility. Implied tenors of toxic elements in the magnetite may represent a serious hazard to environmental and health security. The results inferred from magnetic anomalies support the applicability of the geophysical approach in order to locate high concentrations of iron-rich particles both at surface and below ground and the usefulness of joint evaluation of magnetic susceptibility and ground-penetrating radar in order to characterize the sedimentary and geomorphology-controlled magnetite distribution.