GNGTS 2014 - Atti del 33° Convegno Nazionale

124 GNGTS 2014 S essione 2.2 surface geology was reconstructed joining the available geological and geophysical data. Noise measurements were used to constrain the upper portion of the subsoil along the transect. Geological settings. The historical center of L’Aquila is founded on a fluvial terrace at about 60-80 m above the Aterno river bed. The slopes along the flanks of the L’Aquila terrace are generally steep with a mean value of about 36% and a local maximum scarp of 120%. According to the Italian Building Code (NTC, 2008) the topographic amplification factor S T is on average equal to 1.2, even though it can reach locally S T = 1.4. Fig. 1 shows the geological map of the area, as developed by the Seismic Microzonation studies (����� ������� ������ ������ ��� MS–AQ Working Group, 2010). The city is boarded to the West and the South by the Aterno river valley covered by actual fluvial and terraced alluvial deposits. The North and the East of the village are surrounded by mountain and hill ranges formed by Meso-Cenozoic limestone rocks and Miocene flysh units. The terraces are formed by ������ ����������� ����������������� ���������� �������� ��� ���������� ������ middle Pleistocene variably-cemented calcareous breccias and calcareous gravel sediments (L’Aquila breccias Auct., Blumetti, 1995). Its thickness as testified by deep boreholes (Amoroso et al. , 2010) ranges from 100 m or more in the northern sector of the city centre to 0- 10 m in its southern zone (i.e. Aterno river). The L’Aquila breccias lie on an about 200 m-thick lower Pleistocene-upper Pliocene (?) fluvial-lacustrine deposits which mainly consist of pelite and sand lithologies. ��� ��������� ���� ����� �� ��� ������������ ������� �� �������� �� ���� The uppermost thin layer of the near-surface geology is composed by soft materials, mainly represented by residual soils known as “red soils”, weathered breccias or anthropic filling material. The red soils are a fine-grained deposit which cover or are interposed within the L’Aquila breccias. The thickness of the red soils can reach 20-30 m in the southern part of the town and along its scarps (i.e. Porta Rivera, Saint Apollonia, Porta di Bagno, Porta Napoli and Collemaggio trenches; Fig. 1), as confirmed by many site campaigns. ��� ���� The man- made fills have maximum thickness of ≈ 8-10 m and they mainly consists of disposal materials such as rubbles of masonry buildings destroyed in past earthquakes. The continental deposits are overimposed to the Meso-Cenozoic carbonate substratum. Its depth ��������� ������ �� decreases toward NE as testified by ���� ��������� ��� ����������� ��� ������� ���������� �������������� �������� deep boreholes and gravimetric and seismic reflection investigations (Amoroso et al. , 2010; MS–AQ Working Group, 2010; ������� Tallini et al. , 2011; ��� ������ Del Monaco et al. , 2013� ��� ) and it outcrops in the northern part of L’Aquila hill. Data and methods. The whole studied area (Fig. 1) counts a lot of geological, geotechnical and geophysical ��������������� ����� ���� ���� �� ���� ���� �� ������������ ��� ����������� investigations, which were used in this work to characterize the sub-surface geology of the area such as the geometry of the bedrock at depth, the geotechnical property of the soft layers and ��� ������� ���������� �������� ����� �� � ����� ���� ����� �������������� the related shear-wave velocity (Vs). In a large part those investigations were promoted by the Department of Civil Protection (MS–AQ Working Group, 2010) for seismic microzonation studies; the deep boreholes in the historical centre were promoted by the University of L’Aquila – Centre for Research and Education in Earthquake Engineering (CERFIS) �������� (Amoroso et al. , 2010; ���������� � �������� ������ ��� ���� �������������� ���� Cardarelli e Cercato, 2010� ��� ���� �������������� ���� ), the deep investigations were promoted by ENI (Italian oil and gas company) for the seismic reinforcement and rebuilding project of Santa Maria di Collemaggio Basilica (AA.VV ., 2013), and further investigations carried out for the reconstruction of private damaged buildings (Totani et al. , 2012; Monaco et al. , 2013; Amoroso et al. , 2014). In particular, the available data (Fig. 1) consist in: �� ����� ��� at least one hundred boreholes to 20-35 m depth, eight deep boreholes to 50-270 m depth, twenty down-hole tests to 30-50 m depth, one cross-hole test to 80 m depth, five seismic dilatometer tests to 5-17 m depth, four seismic dilatometer tests in a backfilled borehole to 50-80 m depth, few resonant column/cyclic torsional shear tests, and several surface wave tests, electrical tomography surveys seismic noise measurements. In addition, seven temporary stations (AQ04, AQ09, PAOL, AQ01, NAPO, AQ03, AQ11) were installed in the southern edge of L’Aquila after the April 6, 2009 within the microzonation activities, that recorded earthquakes from May 28, 2009 to July 2, 2009 (MS–AQ Working Group, 2010; Milana et al. , 2011; white triangle in Fig. 1). These available data confirm the subsoil conditions are quite complex. L’Aquila terrace is characterized by a shear wave velocity V S inversion at the transition from the calcareous breccias with highly variable cementation ( V S ≈ 600-1200 m/s) to the underlying fluvial-