Seismic microzonation studies by using the equivalent linear approach (L’Aquila, central Italy)

This contribution is part of the third level Seismic Microzonation project activities carried out on pilot areas of L'Aquila Municipality area and financed by the Abruzzo Region (Department of Government of the Territory and Environmental Policies - Risk Prevention Service of Civil Protection). L’Aquila Municipality area pertains geologically to the middle Aterno River intermontane basin which was filled up by Plio-Quaternary coarse- and fine-grained detrital deposits related mainly to lacustrine, slope and alluvial environments. It is characterised furthermore by a notable seismic hazard as showed by the recent April 6, 2009 Mw 6.29 near source earthquake and the far field Central Italy 2016 seismic sequence. According to the Italian Civil Protection Department guidelines numerical maps and database were produced at the end of the third level Seismic Microzonation project. The project was realized through the following activities: (i) update of database concerning boreholes, geotechnical and geophysical in-situ investigations; (ii) far field and near source seismic input selection; (iii) computer code selection; (iv) geophysical and geotechnical soil characterization; (v) definition of the geological sections; (vi) 1D and 2D modelling; (vii) mapping the third level Seismic Microzonation zones based on the calculated Amplification Factors; (viii) third level Seismic Microzonation numerical maps elaboration. Considering the complex seismostratigraphy of L'Aquila Municipality area, 2D modeling was carried out on a very large number of sections to calculate in-depth the AFs and analyze their areal variation. The nonlinear soil behaviour is taken into account by performing equivalent linear simulations. The validity of 2D modelling was confirmed by the congruence between the geological background and the AFs value distribution. The 2D modelling allowed to verify the existence of basin and basin edge effects via the comparison with 1D simulations (Preturo-Sassa area). In the Bazzano-Monticchio area crossing the Aterno R. plain, the AF values increase for the intervals of the higher periods which could be possibly linked to 2D effect.