Soutenance de thèse de Rodrigo Yanez

In regions of low to moderate seismicity such as France, the scarcity of instrumental records of large earthquakes hinders reliable seismic hazard assessment. In these contexts, understanding preinstrumental earthquakes is particularly important. To address these limitations, this thesis develops a method for reconstructing the spatial distribution of ground motion intensity during past earthquakes using historical damage data from a limited number of monumental buildings. The case studies are the two largest earthquakes known to have affected the Mugello Basin (Northern Apennines, Tuscany, Italy): the 1542 event (M5.9) and the 1919 event (M6.3). The analysis uses six bell towers that sustained different degrees of damage during these earthquakes. 

The research begins with a critical review of historical damage data—primarily textual descriptions contemporary to the events, complemented in some cases by photographs and building stratigraphy studies. Damage severity is then assessed by assigning damage states using a scale specifically adapted to bell towers. To interpret this damage in terms of seismic demand, numerical structural models of the towers were developed. Finite Element Method (FEM) models were assembled with a detailed representation of the bell chamber, which was the most heavily damaged part of the towers during the earthquakes. The rest of each tower was modelled in a simplified manner, as it sustained either no damage or only minor damage. Material properties were estimated through vibration-based model updating and visual inspection. A simplified nonlinear constitutive law was developed to represent the seismic behaviour of historic masonry. The models were designed to be sufficiently detailed to distinguish between different damage states, while remaining computationally efficient. This balance was essential to allow for the execution of hundreds of dynamic simulations required to perform seismic fragility analysis, accounting for signal-to-signal variability in ground motion. The fragility curves obtained, enabled the translation of observed damage states into probable ground motion intensity intervals, expressed as peak ground acceleration (PGA). The analysis used a collection of real accelerograms compatible with the seismotectonic context of the Mugello region. The results provide probability distributions of PGA for each bell tower site for the 1542 and the 1919 earthquake.

Composition du jury :

• Francesca DA PORTO - Professor, Università degli Studi di Padova - Reviewer 
• Philippe GUEGUEN - Research Director, Université Grenoble Alpes - Reviewer 
• Maria Paola SANTISI - Associate Professor, Université Côte d’Azur - Examiner 
• Antoine MOCQUET - Professor Emeritus, Université de Nantes - Examiner 
• Jérôme FORTIN - Research Director, Ecole Normale Supérieure de Paris - Examiner