Local scale seismic landslide susceptibility assessment based on historic earthquake records combined with accelerometer monitoring and ambient noise data

Uncertainty in the quantification of earthquake loading poses one of the major difficulties in local scale seismic landslide susceptibility assessments. This problem can be exacerbated for slope settings that are likely to produce considerable amplifications of seismic shaking. We address this issue by examining the case of a historic landslide triggered by the 1627 Apulian (southern Italy) earthquake (epicentral intensity X on the MCS scale) in the peri-urban area of Caramanico (central Italy), distant ~120 km from the epicenter. The failure caused a large downslope displacement and destroyed several buildings. The slope seismic response is assessed using data from long-term accelerometer monitoring of the hillslope and from recent ambient noise measurements. This provided evidence of significant directional amplifications, e.g., by a factor of approximately 4 and 20, respectively in terms of peak horizontal acceleration and Arias Intensity during the 2009 Mw 6.3 L’Aquila earthquake that occurred 60 km NW of Caramanico. Then taking into account the site amplification, permanent displacements are calculated by applying a rigorous Newmark approach. This study shows that historical information on landslides triggered at apparently anomalously large distances from an earthquake epicentre can help to identify hillslopes influenced by site effects and that reconnaissancetype measurements of ambient noise can be useful to reveal directional amplifications. The importance of accurate assessments of other relevant input parameters (e.g., material properties, slip surface geometries, groundwater conditions) used in seismic slope modeling is also recognized.