Tracing the seismic history of Sant’Agata del Mugello (Italy, Tuscany) through a cross-disciplinary approach

International audienceHistorical seismicity is mainly defined from historical sources which are not always available. Yet historical buildings are a unique opportunity to record and study effects of past earthquakes at a given place. An innovative methodology is defined to improve knowledge of local historical seismicity. Such a methodology is based on an interdisciplinary approach combining: analysis of historical sources, stratigraphic analysis and structural analysis of an historical building. The church of Sant’Agata del Mugello (Italy, Tuscany) is considered as a case of study. The stratigraphic analysis is performed by identifying the repairs using the RECAP methodology. 80 repairs units using 13 building techniques are identified in the church. The identified repairs are associated with unknown events, earthquakes or routine reconstructions. When post-earthquake reconstructions are found, damage mechanisms are associated with them. 13 constructive phases of the church have been traced combining stratigraphic analysis and historical sources. A proto-church was built before 948 A.D. and is nowadays below the current one. The first phase of the current church appears between the 9th and the 12th century. A significant event of unknown origin occurred during the 12th century which probably led to an important collapse and then a significant reconstruction of the church. The church is then deeply affected by the 1542 seismic event (epicentral macroseismic intensity 9, deduced magnitude 6.02) which resulted in the collapse of the upper part of the bell tower and the two lateral chapels as well as the overturning of the front wall and of the two lateral walls of the nave. The 1611 seismic event (epicentral macroseismic intensity 7, deduced magnitude 5.1) damaged the upper part of the bell tower as described in historical records. In spite of the confirmed occurrence of seismic events in the area from the middle of the 17th century and the beginning of the 20th century, no information relating seismic damage of the church has been found in historical records nor in the startigraphic analysis. The most important earthquake which struck the area on June 19th, 1919, produced only some small cracks in the church (magnitude 6.38)