Landslides DOI 10.1007/s10346-020-01526-z Received: 1 July 2020 Accepted: 20 August 2020 © Springer-Verlag GmbH Germany part of Springer Nature 2020 Angela Perrone I Filomena Canora I Giuseppe Calamita I Jessica Bellanova I Vincenzo Serlenga I Serena Panebianco I Nicola Tragni I Sabatino Piscitelli I Luigi Vignola I Angelo Doglioni I Vincenzo Simeone I Francesco Sdao I Vincenzo Lapenna A multidisciplinary approach for landslide residual risk assessment: the Pomarico landslide (Basilicata Region, Southern Italy) case study Abstract On 25 and 29 January 2019, a large landslide destroyed an important part of the town of Pomarico (Basilicata Region, Southern Italy). Geological and geomorphological investigations provided a detailed description of the landslide features. Several geophysical surveys were carried out to deepen knowledge of the landslide and the residual risk assessment. Detailed electrical resistivity tomography (ERT), multichannel analysis of surface waves (MASW), and seismic refraction tomography (SRT) have been used to analyze geomorphological evidences of the failure and the potential kinematic evolution of the landslide scarp, a crucial factor to assess landslide residual risk. The joint analyses of the geophysical results, compared with geological and geomor- phological data, allowed to obtain detailed information about the stratigraphic contact between clayey and sandy deposits in the crown area of the landslide, and to identify the post-failure stabil- ity condition changes in sands. The geophysical analyses con- firmed the presence of multiple old degraded scarps developed over time and provided information on the decompression state of the different areas of the landslide crown. The results highlighted a subparallel stratification consisting of an anthropic surface carry- over material, which covers a layer of sands with silty intercala- tions, overlying clayey material that represents the bedrock of the investigated area. Furthermore, natural and anthropogenic caves, mainly developed in well-cemented layers of sands, were identi- fied. This study emphasized how the integration of different geo- physical methods constitutes a capable tool for characterizing landslides, contributing to assessing the landslide residual risk of the slope mass and evaluating the suitability of the methods in relation to the investigated landslide conditions. Keywords Geophysical investigations . Geomorphological analysis . Landslide residual risk Introduction Landslides represent natural processes crucial in the landscape evolution and widely recognized as widespread hazardous phe- nomena able to cause loss of lives and severe damages to proper- ties and to human activities (Glade et al. 2012; Petley 2012). Over the past few decades, because of their significant socioeconomic impacts (Perera et al. 2018), several different investigation methods, technologies, and early warning systems have been de- veloped. They have been applied with the aim of understanding and monitoring the behavior of the landslides, under changing environmental and climate conditions (Casagli et al. 2010; Galeandro et al. 2013; Doglioni et al. 2015; Vassallo et al. 2016; Piciullo et al. 2018; Segoni et al. 2018; Pecoraro et al. 2019). All the investigation methods have been finalized to explain the different elements contributing to landslide hazard and risk as- sessment, which represent the necessary processes to formulate evolution scenario analysis to be followed up by appropriate mitigation strategies. In landslide studies, due to the complexity that characterizes these phenomena, it is necessary to choose the best technologies and the opportune procedures to assure that the selected method- ology is appropriate and successful in agreement with the set of data. The selection of the most appropriate available techniques to investigate the area affected by landslide and to assess residual hazard or risk of the landslide slope is crucial. There are several suitable approaches: engineering geology surveying (Borrelli et al. 2014; Calista et al. 2019), terrestrial geodetic techniques (Barbarella et al. 2015; Burdziakowski and Tysiac 2019), remote sensing (Calò et al. 2014; Doglioni et al. 2016; Crosta et al. 2017; Casagli et al. 2017; Frodella et al. 2018), and geophysical prospecting (Jongmans and Garambois 2007; Perrone et al. 2014; Pazzi et al. 2019; Whiteley et al. 2019). The choice of the best approach may vary according to the specific situations and depends on several factors, primarily on the geostructural and geomorphological setting of the area, on the landslide typology and geometry, on the slope stability conditions, and on the state of activity (Cruden and Varnes 1996; Spilotro et al. 2017). In the last decades, geophysical methodologies have largely been recognized as reliable and effective for landslide investiga- tions and for the characterization of landslide-affected areas (Jongmans and Garambois 2007; Perrone et al. 2014; Pazzi et al. 2019). Applications of different geophysical surveying methods, such as geoelectrical, seismic, and electromagnetic, are widely present in landslide-related literature (Lapenna et al. 2005; Wang et al. 2016; Calamita et al. 2019). Large areas of the Italian territory result seriously affected by landslide phenomena, and the Basili- cata Region (Southern Italy), characterized by a high density of landslides, represents one of those areas (Trigila et al. 2010; Lazzari et al. 2018; IFFI Project 2020). In Basilicata, landslides often affect historical settlements built on hills that are frequently character- ized by slope instability processes controlled by different predis- posing factors, such as lithology, geomorphological and structural setting, and topographic factors. These phenomena are mainly induced by several natural and anthropic triggering factors, as well as the recent effects of the climate change, causing more frequent heavy rainfall events, and land-use changes (Polemio and Sdao 1996, 1998; Lazzari et al. 2013), determining severe hazard and risk levels. The latest important rainfall-induced landslide occurred in the urban area of Pomarico village (Doglioni et al. 2020), located in the hills close to Matera between 450 and 380 m a.s.l., along a narrow ridge between the Basento and Bradano river Landslides Recent Landslides