Anthropogenic Sinkholes in Umbria (Central Italy): Georeferencing of underground cavities and Cavity density Maps for some urban areas

Abstract

Anthropogenic sinkholes represent a significant hazard in the historic centres of Umbria (Central Italy), where extensive but often undocumented hypogean cavities may undergo progressive degradation and failure. This study aims (i) to test the spatial relationship between anthropogenic underground cavities and documented sinkhole occurrences, and (ii) to provide a descriptive regional overview of the distribution of both underground cavities and anthropogenic sinkholes. To this end, an updated regional inventory of anthropogenic sinkholes was integrated with a georeferenced GIS database of underground cavities to support first-order susceptibility screening in urban areas. The official ISPRA sinkhole dataset was expanded by incorporating recent events derived from local news reports, whose locations were refined through address-based georeferencing and visual cross-checking using Google Street View, increasing the inventory from 60 to 75 recorded cases. A multi-source survey compiled 180 anthropogenic cavities across 11 Umbrian towns, classified by primary function and associated with qualitative positional confidence. Kernel Density Estimation (KDE) was applied to towns with sufficiently dense datasets (Perugia, Terni, Orvieto, Assisi, Gubbio, and Todi) to produce cavity-density maps highlighting spatial clustering within historic urban fabrics. Results show that the highest cavity densities systematically coincide with historic cores, reflecting long-term underground use and suggesting a close spatial association with reported sinkhole occurrences. While not intended as probabilistic hazard models, the KDE-derived density maps provide an effective screening tool for identifying areas of potential subsurface instability, supporting urban planning, and improving the management of underground cultural heritage in data-limited contexts.