Speleoseismology in the Dinaric Karst of Slovenia

Cave sediments may be used not only as an archive for past climate changes but also as an important and until recently an overlooked archive for seismic events. This has been done in many karstic areas around the world, but not in the Dinaric Karst area of Slovenia making this study a pioneer work. The Dinaric Karst covers the area between the Ljubljana Marsh (Slovenia) to the east and the Bay of Trieste (Italy) to the west and Rijeka (Croatia) to the south. There are around 6,000 known and explored caves and other karstic phenomena in this area that covers approximately 6,400 km2 or 27% of the territory of Slovenia. In the present study, speleothems from several caves in the Slovenian part of the Dinaric Karst area are sampled (more than 90 samples were taken and anlysed) and so far 34 were dated using the radiometric U/Th method. More dates are expected but were delayed due to the COVID-19 pandemic. The sampling was based on conditions which exclude deformed speleothems other than seismically deformed ones therefore validating the samples as records of paleoearthquakes. Two clusters in space and time (around 3kyr BP and 10kyr BP) could be identified from our results. Therefore, further to the 1511 magnitude 6.9 historical earthquake sequence the Dinaric Karst in Slovenia was most likely affected by two newly inferred large paleo earthquakes.