Geoscientific investigations for mapping the subsidence risk in an urban area

The geomorphological characteristics of the Salento peninsula (Puglia, south-eastern Italy) mean that movements of mass are extremely rare. These phenomena particularly affect certain coastal zones characterized by cliffs in rapid retreat and some unusual points in the hinterland in which collapses, generally linked to the development of karstic cavities, are common. These phenomena demonstrate the brittleness of some areas of the Salento and they constitute a restraint on the use of the territory itself. The town of Nardò is one of the sites at greatest geological risk in the Salento peninsula. In the last few decades, the historical centre of Nardò has been affected by a series of subsidence events, which have, in some cases, resulted in the partial collapse of buildings and road surfaces. These events have had both social repercussions, causing alarm and emergency situations, and economic repercussions in terms of the expense of restoration. In order to determine the causes of the ground subsidence events, integrated geophysical surveys were undertaken in the historical centre of Nardò. In addition, the historical succession of the subsidence events seen over the last 50 years was reconstructed, with the purpose of estimating the dimensions of the phenomenon and its possible relationship with specific environmental conditions (for instance intense precipitation). The study led to the production of a ground subsidence risk map of a sample area and made it possible to determine the real dimensions of the problem and to identify its causes. © 2007 Nanjing Institute of Geophysical Prospecting.