HVNSR survey in historical downtown LʹAquila (central Italy): Site resonance properties vs. subsoil model

This paper presents and discusses the results of a detailed seismic noise survey carried out in historical downtown LʹAquila after the earthquake of 6 Apr. 2009 (Mw = 6.3). Seismic noise data were interpreted through numerical simulations, with the support of a subsoil model, characterised by four main units, from the top to the bottom: (i) soft soils (anthropogenic filling material and terra rossa); (ii) LʹAquila breccia; (iii) LʹAquila pelite and sand; and (iv) the Meso-Cenozoic carbonate bedrock. NSR analysis permitted the identification of two peaks (f0 and f1) nearly everywhere. f0 (0.4–0.7 Hz) is due to the superposition of LʹAquila pelite and sand on the carbonate bedrock at 200–300 m below ground level. f1 (3–15 Hz) is caused by shallower impedance contrasts due to 3–20 m thick soft sediments overlying LʹAquila breccia and by the weathering profile of LʹAquila breccia. rical simulation was carried out for three different models characterised by: (i) lithology lateral variation in the first 100 m of thickness due to the substitution, from north to south, of LʹAquila breccia with LʹAquila pelite and sand; (ii) the thickness variation of soft top soil onto LʹAquila breccia; and (iii) the presence of a weathered layer in the upper part of the LʹAquila breccia. The numerical simulation results fit the experimental seismic noise data. ial correlation between areal distributions of severe damages with that of f1 resonance frequency is found. So it follows that the severe damage during the LʹAquila earthquake of 6 Apr. 2009 could have been caused by the seismic local effect of the soft top soil and the weathering profile of LʹAquila breccia.