Seismic microzonation of an alluvial valley hit by the 2016 Central Italy earthquake

Between August and November 2016, a seismic sequence, with magnitude, Mw, ranging between 5.9 and 6.5, struck the Central Italy. The paper discusses the results of the seismic microzonation study of two hamlets, Pretare and Piedilama, heavily damaged by this seismic sequence. The two villages are located in an alluvial valley, where large landslide bodies and loose soil layers cover a severely deformed Flysch bedrock. The experimental data collected during the field and laboratory investigations allow defining a 2D model of two representative cross sections of the valley. Their seismic response was evaluated carrying out nonlinear dynamic analyses. The response of the valley was synthesized in terms of amplification factor of the spectral acceleration, computed in three different ranges of periods. The results show that the maximum amplification factors are detected along the central part of the valley, due to both high impedance ratio and 2D basin effects.