Constraints on long-term seismic hazard from an intact, vulnerable stalagmite for the surroundings of Ördöglik (Čertova diera) part of Domica cave, Slovakia

To verify seismic hazard maps by independent observations that serves long-term information should be necessary. It requires studying vulnerable dripstones, since they survived all earthquakes that have occurred over thousands of years, depending on the age of them. Examination of an intact vulnerable stalagmite (IVSTM) in Ördöglik part of Domica cave (Slovakia) has been done. This IVSTM is suitable for estimating the upper limit of horizontal ground acceleration (HGA) generated by prehistoric earthquakes. This research is the continuation of our previous examination of IVSTMs in Baradla and Domica cave system, north-east Hungary.

               The density, the Young’s modulus and the tensile failure stress of the samples originating from broken speleothems have been measured in geo-mechanical laboratories, whereas the dimensions and natural frequency of the IVSTM was determined by different types of in situ observations. The value of HGA resulting in failure and the natural frequency of the IVSTM were assessed by theoretical calculations. The ages of the samples taken from a column next to the investigated IVSTM at different heights have been determined by MC-ICPMS analysis. The measured ages fall between about 7.6 and 2.4 kyr. The critical HGAvalues as a function of time going back into the past determined from the stalagmite that we investigated are presented. Our results show that all values of probabilistic seismic hazard maps, SHARE Map (Giardini et al. 2014) and PSHA Map (Tóth et al. 2006) at the location of Ördöglik part of Domica cave, are above the critical horizontal ground acceleration (CHGA) curve calculated by using the dimensions, geo-mechanical and elastic parameters of IVSTM, and the values of CHGA caves are lower than 0.05g since 2.7 kyr (0.05g was estimated by Szeidovitz et al. (2008) using another vulnerable stalagmite 4 km far from Ördöglik, in the Baradla cave.) All these means that the seismic hazard is overestimated at the territory of Ördöglik, Domica cave.

               This result have to be taken into account when calculating the seismic potential of faults near to Ördöglik part of Domica cave (e.g. Darnó and Rozsnyó lines).