A comparison between physically-based models and a semiquantitative methodology for assessing susceptibility to flowslides triggering in pyroclastic deposits of Southern Italy

Abstract

Two well-known physically-based models, SHALSTAB and SINMAP, and a statistical approach have been applied to predict the susceptibility to flowslides in the pyroclastic cover of carbonatic ridges in Campania (Southern Italy). The results obtained with these different techniques, specifically concerning the prediction of potential source location, have been compared to explore potential applications and limitations. The statistical approach has been applied to a database of 187 historical flowslides, whose characteristics have been analysed by means of a Semi-Quantitative Method (SQM). The statistical approach has produced more conservative results, by attributing high level of susceptibility to larger areas; moreover, it has proved to be more accurate in predicting the locations of the historical source areas of shallow landslides (i.e. of the real cases analysed). On the contrary, physically-based models have resulted more effective in considering the effects of local morphology, such as channels and convergent areas, but less accurate in predicting triggering locations on either planar or divergent slopes. The primary limitation of the adopted SQM is that it relies on subjective input data. On the other hand, the physically-based models emphasize the effects of topography, by assuming steady-state hydrologic conditions and slope-parallel flow within the soil cover. A further drawback of the physically-based models is that they strongly rely on soil hydrologic and geotechnical parameters which are commonly difficult (and expensive) to quantify over large areas.