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.