The use of speleothem damage and in situ fault displacement monitoring to characterise active tectonic structures: an example from Západní Cave, Czech Republic

Povzetek

The EU-TecNet fault displacement monitoring network records three-dimensional displacements across specifically selected tectonic structures within the crystalline basement of central Europe. This paper presents a study of recent and active tectonic fault displacement recorded at Západní Cave in northern Bohemia (Czech Republic). It extends previous geological research by measuring speleothem damage within the cave and monitoring displacements across two fault structures within the Lusatian Thrust Zone. The measured speleothem damage, which are characterised by strike-slip movements, show dextral strike-slip displacement along the WSW-ENE striking fault and sinistral strike-slip displacement along the NNW-SSE striking fault. It is found that the compressive stress σ₁ is located in the NW or SE quadrant while the tensile stress σ₃ is oriented perpendicular to σ₁, i.e. in the NE or SW quadrant. The results of fault displacement monitoring show a long-term dextral strike-slip trend along the WSW-ENE striking fault while the NNW-SSE striking fault presents evidence for uplift of the eastern block. There are notable periods of increased geodynamic activity, referred to as pressure pulses, in 2008, 2010-2011, and 2012. The significant correspondence between the measured speleothem damage and the results of fault displacement monitoring confirm the supposition that, at this site, the compressive stress σ₁ persists in the NW or SE quadrant. The presented results offer an insight into the periodicity of pressure pulses, demonstrate the necessity for protracted monitoring periods as a means for better understanding geodynamic processes, and show that it is possible to characterise the displacements that occur across individual faults in a way that cannot be accomplished from geodetic measurements made using Global Navigation Satellite Systems.