Narrow Results

Elemental concentrations of Sr, Fe, Zn and Cr have been measured by in-air and microbeam PIXE to track the changes during the stalagmite growth. The objective was to find the optimal parameters for the measurements of available isotope-dated stalagmite cuts from Slovenian Karst. Significant concentration fluctuations of Fe, Sr and Cr at the scale of several millimetres have been observed by in-air PIXE. Fluctuations of trace elements observed by microbeam PIXE are contributed to the sub annual periods of growth. As demonstrated, a two-dimensional Ca, Sr, Fe and secondary electron mapping is required to avoid regions with mineral inclusions and surface irregularities during line scans over the speleothems. Optimal measuring parameters for microbeam PIXE mapping of large stalagmite cuts already mapped by isotope dating are given. These measurements would account for sub-annual growth fluctuations.

Is it really plausible that earthquakes break speleothems? May unbroken speleothems prove that no strong earthquake has ever occurred during a certain period of time? The mechanical behaviour of speleothems has been investigated through static bending tests performed on stalactites and soda straws. These tests give an indication not only of the mean tensile resistance, but also — more importantly — of its variation. In fact, it is this variation that makes it difficult to estimate the acceleration necessary to break an individual speleothem. That is why a statistical approach is mandatory. The potentially most vulnerable unbroken as well as broken stalactites were measured in a pilot cave (Milandre, Switzerland). Four classes of stalactites were defined, according to their shapes. For each of these classes, a vulnerability curve (probability of breaking as a function of peak ground acceleration) was obtained by means of a Monte Carlo simulation. Dynamic amplification as well as heterogeneity of bending resistance within each speleothem were taken into account. Finally, an original statistical approach, valid for incomplete and imprecise data, was developed. This approach allowed to estimate the probability that at least one moderate earthquake has occurred in the past.