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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]

We present the geological map at 1:25,000 scale of the Plio-Quaternary Paganica-San Demetrio-Castelnuovo Basin corresponding to the epicentral area of the 6 April 2009 Mw: 6.29 L'Aquila earthquake. The map focuses on the relationships between the active tectonics and the Plio-Quaternary deposits and on the early evolution of this continental basin. Fine-scale geological field surveys, coupled with paleontological data, facies analyses, well logs and geophysical data interpretation, allowed to better understand the stratigraphy and to review the previously described stratigraphical units, resulting in the definition of eight synthems, spanning from late Piacenzian to Holocene. More precisely, the occurrence of a Caspiocypris species flock (ostracods) at the base of the sedimentary infill of the basin formed by a lacustrine system, suggests that the onset of deposition started in the late Piacenzian. The lacustrine system disappeared around the Gelasian/Calabrian transition, while the subsequent evolution of the sedimentary basin was characterized by the presence of fluvial and alluvial fan systems progressively entrenched into the lake deposits. The results of the above-mentioned activities are summarized in the attached geological map, where the Plio-Quaternary synthems and the active normal faults accountable for the significant seismicity were highlighted. [ABSTRACT FROM AUTHOR]