Unearthing earthquakes in the Sienese “Crete”

Abstract

The Val d'Orcia is one of the latest Italian entries (2004) of the UNESCO World Heritage List. Its distinctive landscape of rolling chalk hills (the Crete), shaped in the 14th and 15th centuries to reflect an idealized model of good governance, and celebrated in the paintings of the Sienese school, has become an icon of the Renaissance that profoundly influenced the development of landscape thinking worldwide. Preserving the cultural wealth embodied in this corner of Tuscany is also a matter of assessing its seismic hazard correctly. As a first step toward this end, we revised the local seismic history. According to the current national catalogue, the Crete are a lowseismicity area intervening between two earthquake clusters centered on Siena (north) and Mount Amiata (south); the local earthquakes on record are very few, with middle to low epicentral intensities and none earlier than the second half of 17th century. However, the fortuitous discovery of a recent (1802) damaging earthquake unrecorded by any of the extant catalogues suggested that the current interpretation was more likely to derive from the little interest shown in the area having by previous studies rather than from an actual lack of data. By retrieving the memory of several forgotten damaging earthquakes (from 1449 onwards) and increasing the data set of the already known events, our study does significantly improve the Crete seismic history.