Dynamic characterization of the Eiffel tower

The Eiffel tower is the most visited monument in the world. Millions of visitors have taken millions of pictures of it over the last century but apparently a dynamic picture (that is a dynamic characterization) does not exist or is not publicly available. In this paper we show the amount of information that can be extracted from a few recordings of ambient tremor collected on the tower and on the surrounding subsoil with a single pocket seismometer in a few minutes, during a leisure visit. We also propose a numerical model for the tower, capable to fit the observed data. This is interesting because the mass and stiffness distribution of the tower is unique and does not follow any modern construction rule. The dynamic model of the tower would also be important if Paris were a high seismic hazard town, which is not. According to our model, the tower could withstand peak ground accelerations >100% larger than the values prescribed by current seismic hazard estimates. Regarding the wind, Eiffel could only study its effects from a static planar point of view, while the model allowed us to follow a 3D approach and to assess the expected displacements under different loads. Last, the dynamic model of the tower is also important to better design the future interventions and to monitor the ageing of the structure.