Intact and vulnerable speleothems can be investigated in situ to estimate an upper limit of prehistoric peak ground acceleration. It is possible to say that intact speleothem was not loaded by horizontal acceleration higher than the value of horizontal acceleration resulting in failure, which is assessed by theoretical calculations. Mechanical properties of broken speleothems originating in the same cave are considered for this calculation. In the present paper, determination of the dynamic Youngs modulus of broken speleothems originated in Baradla-Domica cave system (Northern Hungary and Southern Slovakia) is presented. The dynamic Youngs modulus can be calculated based on P and S-wave velocities and bulk density of tested specimens. Two different approaches to determination of bulk density of irregular speleothem specimens are presented - determination of bulk density by standard Water displacement method and by X-Ray Computed Tomography.