Experimental and Numerical Evidence of the Clustering Effect of Structures on Their Response during an Earthquake: A Case Study of Three Identical Towers in the City of Grenoble, France

In this article, interpretation of an equivalent to a macroseismic intensity survey, performed in three identical stand-alone buildings located in Grenoble, France, after an M L 4.1 earthquake, reveals a clustering effect, resulting in different levels of perception of seismic loading by inhabitants. The clustering effect is confirmed using numerical simulation; the variation of the seismic response of the building in the middle of the cluster depends on the azimuth of the seismic source relative to the building cluster. The major effect is the splitting of its resonance frequency, accompanied by a decrease in vibration amplitude. We conclude that clustering has an impact on urban effects, calling into question the validity of seismic design, which considers buildings in urban areas as stand-alone constructions, and the interpretation of macroseismic inten- sity surveys conducted in dense urban areas