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On April 6, 2009, a Mw 6.1 earthquake struck the Plio-Quaternary intermontane L'Aquila-Scoppito Basin in central Italy, causing severe damage to L'Aquila historical downtown and surroundings, which were affected by notable site effects. Previous work has suggested that different site effects may be related to the complex subsurface geologic architecture, given the variable thickness and lithology of L'Aquila-Scoppito Basin filling deposits, on top of which the city was built. To improve the 3D geological model of L'Aquila downtown for seismic site response evaluation and to estimate the seismic hazard of possible buried active normal faults, a multitask project was carried out consisting mainly of the integration of surface geology, geological subsurface datasets and geophysical surveys. Data were interpreted with the aim of creating and building a detailed stratigraphic and tectonic model for the Plio-Quaternary cover of the continental basin and the buried morphology of the Meso-Cenozoic bedrock. We discuss and interpret the results concerning a 1 km-long high-resolution seismic reflection profile and refraction tomography integrated with stratigraphy from deep and shallow boreholes. The results allowed the reconstruction of the Plio-Quaternary succession below L'Aquila downtown. The Plio-Quaternary basin depocentre is located in a minor NNW-SSE graben, an extensional structure within the main regional graben that borders L'Aquila-Scoppito Basin. Finally, data interpretation allowed us to define the subsoil geological model of the study area, to evidence the recent activity of several faults, and to reconstruct the Plio-Quaternary tectono-stratigraphic evolution of the basin. Together, the data are useful to evaluate the seismic hazard of cities with great cultural heritage of central Italy, such as the case study of L'Aquila downtown. [ABSTRACT FROM AUTHOR]

The Castelnuovo village is placed on a small NW-SE trending ridge, approximately 60 m higher than the valley floor, occupying a portion of the larger continental L'Aquila Basin (Central Italy). During the April 6, 2009 L'Aquila earthquake (M w 6.3), the village suffered heavy damage. Several studies investigated the local seismic amplification of the Castelnuovo area employing geotechnical, geophysical, and geological surveys, together with 1D, 2D and 3D numerical models. However, all these studies relied on shallow geotechnical and geophysical surveys, which do not reach the engineering bedrock and do not constrain the presence of an impedance contrast at depth. To date, no detailed study has been carried out to assess the depth of the engineering bedrock. In this work, we fill this gap by executing two deep boreholes reaching the engineering bedrock, tied with an extensive campaign of microtremor measurements all over the Castelnuovo ridge and the surrounding plain. The interpretation of such new data, together with analytical, numerical, and geostatistical techniques, demonstrates that local seismic amplification is linked to a strong impedance contrast at more than 200-m depth beneath the Castelnuovo village associated with the lithological transition between clayey silts and breccias. Such results differ from those provided by previous studies, where such impedance contrast was considered shallower, and represent a milestone for assessing the local seismic hazard of the area. • Castelnuovo village was completely destroyed during the 2009 L'Aquila earthquake. • Previous studies relied on shallow geotechnical and geophysical measurements only. • New deep boreholes allowed to reconstruct depth of the engineering bedrock. • Microtremor measurements identified a sharp impedance contrast at depth. • Seismic amplification is linked to an impendence contrast at 210-m depth. [ABSTRACT FROM AUTHOR]

In this paper we inferred the origin of a huge clastic deposit (i.e. L'Aquila Breccia) which widely crops out within the L'Aquila intermontane basin, a tectonic depression in central Apennines, that is bounded by seismogenic active faults, as demonstrated by the earthquake occurred on April 6, 2009 (Mw 6.1). The genesis of this deposit is still debated in the literature: for this reason, a number of methods have been applied, mainly aimed at evidencing its geomorphological and sedimentological features, as well as at defining its geometry and volume through cross sections constrained by borehole data and field observations. On the basis of the obtained results, we identified such deposit as resulting from a Quaternary rock avalanche event. In particular, the rock avalanche would have detached during the cold climate phases of late Middle Pleistocene from the southern slope of the Gran Sasso Range, a sector characterized by the presence of numerous DGSD-related landforms. We performed morphometric analyses of the Gran Sasso slope, in order to define the potential source area of the inferred rock avalanche and, according to the results, the volume estimated from this area (about 108 m3) is coherent with the volume calculated for the preserved rock avalanche deposit. Furthermore, we analyzed the main features of the deposit (i.e. age and morphometric parameters) also in the light of similar rock avalanche events occurred in the same region during the Quaternary, with the aim of discussing potential analogues and better understanding the role of gravity-induced processes in the Quaternary morpho-evolution of the Apennine chain. Unlabelled Image [ABSTRACT FROM AUTHOR]