Neolithic stone settlements as locally resonant metasurfaces

TL;DR

This study reveals that Neolithic menhirs act as low-frequency resonators, and demonstrates their potential use in seismic metasurfaces for ground vibration mitigation, combining seismic noise analysis and numerical modeling.

Contribution

It introduces a viscoelastic model explaining the resonances of menhirs and explores their application in seismic metasurfaces for earthquake engineering.

Findings

Menhirs exhibit fundamental resonances between 10-25 Hz.

Numerical simulations confirm bending and other resonances in the 25-50 Hz range.

Resonance behavior suggests potential for seismic vibration mitigation.

Abstract

We study the dynamic surface response of neolithic stone settlements obtained with seismic ambient noise techniques near the city of Carnac in French Brittany. Surprisingly, we find that menhirs (neolithic human size standing alone granite stones) with an aspect ratio between 1 and 2 periodically arranged atop a thin layer of sandy soil laid on a granite bedrock, exhibit fundamental resonances in the range of 10 to 25 Hz. We propose an analogic Kelvin-Voigt viscoelastic model that explains the origin of such low frequency resonances. We further explore low frequency filtering effect with full wave finite element simulations. Our numerical results confirm the bending nature of fundamental resonances of the menhirs and further suggest additional resonances of rotational and longitudinal nature in the frequency range 25 to 50 Hz. Our study thus paves the way for large scale seismic metasurfaces consisting of granite stones periodically arranged atop a thin layer of regolith over a bedrock, for ground vibration mitigation in earthquake engineering.