Recent micro-tectonic movement from three karst caves, Slovenia

Monitoring of micro-tectonic movement in Postojna cave started in 2004 and in Polog and Kostanjevica caves in 2008. In Postojna cave two TM 71 extensometers, 260 m apart, are installed at the same fault zone, which extends about 1 km north from the Dinaric oriented (NW-SE) Predjama Fault. Since 2004 to the present small tectonic movements are detected, dextral horizontal movement of -0.05 mm for Postojna 1 and extension of -0.03 mm for Postojna 2. But the highest peaks can be of 0.08 mm. Preliminary results in Polog cave, where TM 71 is placed in the vicinity of 1998 (Mw=5.6) and 2004 (Mw=5.2) earthquakes on the Ravne Fault, show -0.08 mm of extension between two limestone beds (from October 2008 to March 2009). From March to May 2009 the movement on x-axis returned back to -0.02 mm. The highest trend in Kostanjevica cave was detected as vertical movement along z-axis for +0.035 mm from June 2008 to May 2009, representing subsidence of the NW block and uplift of SE block. In all three studied caves the data obtained by TM 71 monitoring are related to active tectonic movements of wider fault zones of Predjama (Postojna cave), Ravne (Polog cave) and Brežice Faults (Kostanjevica cave).