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We present a fine-scale shallow geological setting and its possible influence on the seismic building behaviour of L'Aquila downtown which suffered many casualties and building damage caused by the 6 April 2009, Mw 6.1 earthquake. This study draws mainly on the integration of 666 borehole logs and 274 microtremor recordings interpolated with GIS-based techniques. The shallow geology of L'Aquila downtown is characterised by Middle Pleistocene calcareous L'Aquila breccias. Their top surface consists of a weathered epikarst zone that is mantled by Red Soil (reddish colluviated Alfisols) formed during the late Pleistocene. The areal distribution and thickness of Red Soil are causative of the medium microtremor frequency (3–13 Hz). The map of cross-correlation between the medium frequencies, estimated through the empirical Eurocode 8 equation, shows buildings with possible seismic coupling due to the shallow geology setting and the fundamental building period. This technique is further supported by the areal distribution of seismic building damages caused by the 2009 and 1703 L'Aquila earthquakes. This approach, carried out with a large geological and geophysical dataset, is useful in defining seismic site effects and may be effective in mitigating the seismic risk of cities with notable historical heritage in Central Italy, such as the L'Aquila downtown area. [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]