Seismic Vulnerability of a Slender Intact Stalagmite standing in a Karstic Cave

Recently, it has been argued that natural, intact stalagmites in caves give important constraints on seismic hazard since they have survived all earthquakes over their (rather long) life span. For this reason, applying detailed modelling methodologies to study the seismic motion of speleothems has special significance. Here we present a stalagmite-based study from the Little Carpathians of Slovakia, Plavecka priepast cave.

The seismic response of stalagmite is computed using a robust, a fully three-dimensional, Finite Element Method model calibrated from free vibration records by Hilbert-Huang modal extraction. It is demonstrated that the stalagmite vibrations consist of pairs of closely coupled flexural natural modes with a negligible role of vertical excitations.

An underground record of a moderate earthquake was applied to excite low intensity seismic vibrations. Particular attention was paid to observing the role of the vertical component of seismic ground motion. It is concluded that the failure mode of the stalagmite is driven by flexural vibrations. The safety margins of this stalagmite were assessed by analysing the tensile stress map from the seismic response computations. The location of the breaking point of the stalagmite is a result of a balance between the overturning bending moment and variations of horizontal cross-sections with height. The ultimate peak velocity of excitations equalling 3.2 mm/s is estimated.

The used input data and the animations are available on these web pages:

https://z.zembaty.po.opole.pl/SupplementaryStalagmite3Dview.html

https://z.zembaty.po.opole.pl/SupplementaryStalagmite.html