Landslides triggered after the 16 August 2018 Mw 5.1 Molise earthquake (Italy) by a combination of intense rainfalls and seismic shaking

On 16 August 2018, a Mw 5.1 earthquake occurred in the Molise region (Central Italy) during an intense rainfall event which cumulated up to 140 mm in 3 days. Within 5 days after the seismic event, 88 landslides were surveyed and classified in disrupted and coherent as well as in first-time failures and reactivation. As it resulted by the inventorying, most of the surveyed ground effects were represented by coherent landslides involving clays, marly clays, and cover deposits on low dipping slopes. A spatial distribution analysis of landslides in relation to seismic action and rainfall intensity was carried out to evaluate the possible contribution of both the rainfall-induced saturation and the earthquake shaking to landslide triggering. Based on this analysis, in the epicentral area, it is not possible to clearly split the role of seismic and hydraulic destabilising actions, while, at greater distances, the joined contribution of rainfall and earthquake shaking could have promoted slope failures. Comparisons among collected data and existing worldwide catalogues allow to highlight, through the analysis of the spatial distribution of the surveyed landslides, the possible and not negligible effect of soil saturation during the seismic shaking both in epicentral distance vs. magnitude distribution and in number and spatial concentration of triggered ground effects.