The new railway route Divača - Koper is planned to cut through the Karstic thrust edge, a prominent geomorphologic step within the active Adria - Dinarides thrust zone. This represents a major obstacle for the railway construction, therefore it is crucial to understand the structural properties and the geometry of the thrust-fault planes within the area. This knowledge is also important for the calculation of exploitable material in a limestone quarry. For determining thrusts with a low-angle inclination we evaluated the use of the low frequency ground penetrating radar (GPR). We carried out a survey in the active Črnotiče quarry with a 50 MHz rough terrain antenna (RTA), correlated the GPR results with borehole data and constructed a precise 3D model of the Socerb thrust-fault plane. In addition to acquiring accurate structural information about the thrust-fault plane and dip of the strata, we were also able to detect different karst features. When the excavations in the quarry reached the thrust-fault in one part, we found it outcrops exactly where we had previously defined its position. We conducted an additional GPR survey using the 50 MHz RTA as well as a 250 MHz antenna, and obtained new information about the extent and the geometry of the Socerb thrust-fault plane.