The Sinkhole Hazard Study at Casalabate (Lecce, Italy) using Geophysical and Geological Surveys
Abstract
In the last two decades the village of Casalabate was affected by a number of sinkhole events, the last episode occurring on 7 January 2012. Due to some geological and geotechnical uncertainties, Casalabate became an intriguing case study of sinkhole hazard in urban areas and three geological-geophysical models were recently proposed by three different studies. In this paper new geophysical data and some epistemological consideration were done. The results are a contribution to an efficient predictive model that could be well define both the geological setting and sinkhole hazard.
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Introduction
Casalabate is a coastal small town frequently affected by sinkhole events. The first noticed event occurred on 1993 and caused several destructions of buildings. In the same year, a sinking of a small portion of emerged beach happened (Delle Rose and Federico, 2002). Four years later a collapse affected the submerged portion of beach and allowed the formations of a submarine spring, since then the bathing was forbidden for some weeks. Two episodes of sinkhole on the emerged beach occurred during 2000 and 2004, along a strike no longer than 30 meters. Each of these caused on surface short-lived elliptical depression quickly filled by sand. All the aforementioned episodes occurred inside a narrow area (about 250 m long and 100 m wide) close to the coast and oriented according to a north-north-east - south-south-west tectonic structures system (Delle Rose and Leucci, 2010). Further episodes occurred on March 2010, November 2010 and March 2011. The last noticed sinkhole happened on 7 January 2012. Usually the sinkholes occurred during or after rains or sea storms and each episode lasts some minutes at least. Due to geological and geotechnical uncertainties, Casalabate became an intriguing case study of sinkhole hazard in urban areas and three geological-geophysical models were recently proposed to explain the ground-instability and to asses the related hazard (Delle Rose and Leucci, 2010; Calò et al., 2011; Margiotta et al., 2012). 3D geological model and new geophysical data here shown can contribute to an efficient predictive model taking into account the hydrogeology context. Moreover, some epistemological considerations had performed to improve the interdisciplinary exchange between geologists and geophysicists.
Conclusion
The case of Casalabate is a good example of how geological uncertainties can worsen the hazard assessment. In consideration of the complexity of the problem and the concerns of the collectivity, an efficient predictive model of the hazard should be defined. In order to select the most appropriate geological-geophysical model, confrontations among all the researchers working on this issue would be desirable. Especially the knowledge exchange between geologists and geophysicists must be improved. As revealed the ERT and GPR surveys exposed in this paper, dangerous cavities could be placed also out of the area repeatedly interested by sinkholes since 1993. Consequently an efficient predictive model taking into account the hydrogeology and hydraulic context, especially the occurrence of rains and sea storms, must be produced.