Topographic effects in Amatrice suggested from the SiSeRHMap predictive model, seismic data and damage

Amatrice is considered as the "symbol" village of the destructive action induced by the 6.0 and 6.5 magnitude earthquakes, which struck Central Italy on August 24th and October 30th 2016. The village, site to 10km from epicentre, paid the highest price in terms of human lives, injuries, widespread collapses and damage to buildings. Our first field surveys in the Red Zone ascertained that the building collapses or damage was widespread, and involved different building typologies, in different areas, and included new buildings too. We performed a preliminary analysis using the topographic module of SiSeRHMap. The results of this analysis indicated a substantial amplification over most of the hill, with greater values located at the NW end of the promontory and along the top of the steepest slope, where amplification values reached up to approximately 2.0 in the frequency range 2-5 Hz that includes the typical fundamental vibration modes of most buildings. In order to precisely define the effective role of the topographic site effect, two sets of two seismic stations were installed at four critical points in the Red Zone, in two different periods during the seismic sequence. The SSR results, in accordance with those of the HVSR analysis, showed a relevant amplification at the crest station, more than a factor of four taking into consideration the median values. In addition, the directional analysis showed an amplification at 2-3Hz along the transversal axis of the relief, but further amplifications were also recorded at higher frequencies.