Stefan Shanov

Evidence for the existence of a paleosubduction zone beneath the Rhodopean massif (Central Balkans)

Abstract The idea of a paleosubduction zone beneath the Rhodopean massif in the Central Balkans is supported by evidence obtained by the authors. Results from teleseismic studies of the lithosphere in the region, fault plane solutions of local earthquakes and the relevant stress orientation axes, as well as some other geophysical fields measured in the same area, draw a picture of the geologic structure which is most likely a paleosubduction zone. The contemporary seismic activity in this area suggests that the subduction process is not entirely completed yet.

Tectonic Control on Karst Evolution

The tectonic control on the formation of surface and underground karst landforms is described in the literature mostly as an influence of the tectonic structures (anticlines, synclines, faults, fractures) and (or) vertical crustal movements as a precondition to the development of leveled karst. A review of the published works, discussing the tectonic preconditions of karstification, reveals the new qualitative view on the relationships between the geodynamical processes and karst evolution, as well as the importance of the modern quantitative approaches for deeper understanding of these relations. The experience from karst regions in different countries demonstrates that karst systems might be a good marker for arranging in the time the reconstructed tectonic stress fields, in particular for recognition of the Neotectonic and Quaternary stress fields, and vice versa, the reconstructed and recognized as young stress fields can help the forecasting of the preferential directions of the karst galleries formation and the related dominant flow of the karst waters.

Tectonic Stress Fields and Karst

Many natural causes exist controlling the formation of fractures. The rock properties relating to the brittleness is one of the most important of them for the variations in natural fracture density. These properties may vary from regional to local scale; they may vary significantly within the rock formations and between formations. The focus in this chapter is on in situ studies of the fracturing and its relationship to the stress, especially in rocks potentially capable to be karstified (limestones, dolomites, marbles, etc.). The basic concepts of the used methods for reconstruction and analyses of tectonic stress fields are presented. A special attention is given on striations on tectonic slickensides, shear joint systems, electrical anisotropy, and earthquake fault-plane solutions. The evolution of the karst process is discussed as a consequence of tectonic impacts in the geological time. Results from investigations in karst massifs of Bulgaria, Albania, Cuba, and France give a better understanding how the stress fields controls the drainage route and the formation of cavities and cave systems.

Recent Geodynamics and Karst

In this chapter, we discuss the methodological aspects of the paleoseismologic and recent geodynamics research in karst terrains. Till now a complex methodology for comprehensive studies on the relationship “karst—dynamic tectonics” is not approved and methodological apparatus including state-of-the-art techniques as statistical analysis of the deformed karst sediments, monitoring of the recent tectonic movements, measurement of the natural frequencies, and horizontal ground acceleration of speleothems and dating methods is proposed. The elements of this methodology are tested in different karst areas in Bulgaria. The results obtained from field studies in mountainous karst regions of Stara Planina (Balkan) and Rhodopes Mountains support the idea that the karst landforms situated in the downthrown block of the nearby fault are more amenable to tectonic deformations.