Fragile geologic features (FGF) are used as negative indicators of strong ground motion. By evaluating the stability of FGFs and determining their age, it is possible to constrain the local maximum seismic ground acceleration that has occurred during their life time. This methodology was originally developed to analyze precariously balanced rocks (a subset of FGFs), and was used to assess long-term fault activity and improve seismic hazard analyses.

In the Negev Desert of Israel, several in-situ, slender rock pillars exhibit natural frequencies within the range of seismic waves (1-10 Hz), and therefore constitute an important FGF-subset. However, the motion of such pillars may be complex with an initial stage of swaying followed by basal detachment, rocking and toppling or failure within the pillar. To demonstrate that pillar stability can be analyzed using the existing FGF methodology, we show that the tensional stresses developed at the base of a pillar swaying at its fundamental modes of motion and in a pillar deflected to its critical angle, are comparable or larger than the typical tensile strength of Negev pillars.

Finally, we demonstrate how a newly documented dataset of Negev FGFs can be used to provide new insights on fault activity along the Negev-Sinai Shear Zone and the Arava Fault. Assuming a plausible range of motion amplification, the stability analysis yields significant constraints on fault seismicity parameters (M<7 for a section of the Arava Fault). Extending the regional dataset would provide important insights for regional seismic hazard along the Dead Sea Transform.