Complex and spatial analysis of geophysical data recorded in the areas of karst forms developed in horst structures

Abstract

The paper presents the results of geophysical surveys carried out over two voids occurring in limestone in the area of the Zakrzówek horst in Krakow, Poland. The first void was an anthropogenic cavern in the Kostrze site (a district of Krakow), while the second one was the Jasna cave (located in a reserve named “The Twardowski Rocks”). The main terrain surveys were carried out using GPR (ground penetrating radar). To reduce interpretative ambiguity, the GPR results were correlated with additional results obtained from two other methods, i.e. the GCM (ground conductivity meter) and ERT (electrical resistivity tomography). The main aim of the geophysical surveys was the detection and 3D visualisation of karst forms developed around both voids located in horst structures in limestone. The particular purpose of the research was to try to clarify the geological nature of the GPR anomalies characterised by an almost complete lack of reflections, both ohmic and scattering attenuations of GPR signals were analysed to solve the reduction of the reflection amplitudes. Another important fact discussed in the paper was the low consistency and similarity of the results obtained from geophysical surveys carried out above the Jasna cave. The interpretation of the GPR and GCM data recorded over the anthropogenic cavern allowed the places of strong weathering/fracturing of limestone to be indicated as well as a zone of limestone filled with clay-rich material. The interpretation of the GPR and ERT data recorded over the cave made it possible to identify areas of the strong weathering/fracturing of limestone, faults, anastomoses and karst chimneys.