A Comprehensive Seismic Monitoring of the Pillar Threatening the World Cultural Heritage Site Chauvet‐Pont d'Arc Cave, Toward Rock Damage Assessment

Abstract

AbstractFragile geological features must undergo frequent structural health assessments to prevent catastrophic failure events. The mechanical behavior of natural sites is largely guided by vibrations of the earth and environmental exposure, but damage is rarely assessed, except empirically. The Chauvet‐Pont d’Arc cave, a UNESCO World Heritage Site, represents a shining example of fragility that would benefit from monitoring. It is overhung by a rock column known as Abraham's pillar that extends out from the cliff like a natural tuning fork. For this study, we monitored dancing movements of this pillar for over 2 years to analyze its elastic response to weather conditions. Using ambient‐seismic‐noise‐based methods, we identified the pillar's first two natural resonance modes. Through extensive monitoring of the site, we observed the striking temporal evolution of these two resonance frequencies on hourly, daily, seasonal, and pluriannual scales in response to changes in air temperature and insolation. Based on thermo‐acousto‐elastic modeling with a simplified 3D geometric structure, we determined how thermally‐induced stress stiffening affects the rock material, by applying convective and radiative heat fluxes to the model. From the results obtained, we suggest a novel quantitative method based on daily observations that can estimate the level of damage within the rock material. Our work provides a foundation for distinguishing between reversible processes and damage for hazard studies in the frame of climate change. Such knowledge is crucial not only for the preservation of heritage sites but also for enhancing risk assessment protocols and informing conservation efforts worldwide.