Characterization of karst hazards from the perspective of the doline triangle using GPR — Examples from Central Ebro Basin (Spain)

Ground Penetrating Radar (GPR) is a widespread technique to locate and characterise karst hazards (cavities and paleocollapses). In this paper, we show that the internal structure of sediments obtained from GPR surveys can also be used as an indicator of active karst processes. A classification of karst hazard problems by means of GPR in the GPR-doline triangle is proposed, with three end-members: cavities, evidences of subsidence and paleocollapses. These end members show particular signatures in the GPR-profiles. The field examples shown in this paper indicate that GPR survey is a geophysical technique that offers a very high resolution and provides structural and sedimentological information of the subsoil. The use of grid maps, elaborated from GPR data, is an efficient way to determine anomalous sectors (lateral changes of electromagnetic properties, different reflectivity and qualitative penetration depth variations or velocity wave propagation changes). Their relationships with the structural features obtained from GPR-profiles (on-lap geometries, zones with depressed reflectors, folded reflectors or laterally abrupt structural limits) can be used as indicators of karstic processes.