Evaluating site effects in near field conditions for microzonation purposes: the case study of L'Aquila earthquake 2009

L’Aquila earthquake was a complex seismic event characterized by its mainshock on 6th April 2009 with moment magnitude Mw=6.3 and many foreshocks and aftershocks that stroke the whole Aterno River Valley from November 2008 up to September 2009. The huge amount of strong-motion records collected by permanent and temporary stations placed in the valley show a heterogeneous seismic hazard scenario related to different damage levels. With respect to the seismological features of the records within the “crater” (that is the portion of the Aterno Valley that suffered the strongest struck) they show “near field” and “near source” characters although the same records provide differentiated amplification effects among neighboring sites. Geological relieves and direct and indirect in field testing were performed for drawing seismic microzoning maps according to the “Guide Lines for Seismic Microzonation Activity” delivered by the National Department of Italian Civil Protection. As the level three of microzonation studies is concerned, the calculation of amplification factors by means of 1D , 2D and 3D numerical simulations shall be carried out and results summarized within homogeneous seismic amplified areas. This paper focuses on and discusses results from one- and two-dimensional (1D and 2D) numerical simulations at the municipal area of Onna city, destroyed by the main shock on 6th April 2009. It is identified as Macroarea 5. The present study investigate the seismic main characters of the Onna valley response in “near field” conditions. Numerical results have been compared with some strong aftershocks recorded at Onna seismic station lying.