Seismic Micro-zoning in landslide-prone Urban Areas: A GIS Based Instability Assessment at Castelfranci City (Italy)

The present study focuses on a Gis-based strategy to draw Seismic Micro-zoning instability maps in landslide-prone urban areas. As concerns landslide prevention and mitigation policies at the urban scale, the ability of Geographical Information Systems (GIS) to combine multi-layered information with high precision enables technicians and researchers to devote efforts to managing multiple hazards, such as seismically induced instability in urbanized areas. Gis-based Newmark's method is traditionally used for measuring the permanent displacements caused by seismic activity on natural slopes at regional and municipal scales. Hereinafter, the case study of Castelfranci city (Campania, southern Italy) has been studied. This small town, hosting two thousand inhabitants, suffers from the seasonal reactivation of landslides in clayey soil deposits due to rainfall but it is exposed to a high seismic hazard. This study investigates possible seismically induced hazard scenarios within the Castelfranci municipal territory aimed at estimating the slope permanent displacements triggered by the strongest historical seismic event that hit this area: the 1980 Irpinia earthquake. Two simplified relationships relating peak ground acceleration and Arias intensity to permanent displacements have been used and compared. Both equations gave similar permanent displacement values: the two analyses pointed out that multiple portions of both active and quiescent landslide bodies within the Castelfranci urban area can be moved by tens of centimeters generating a high-risk scenario for structures and persons.