Damage mechanisms in masonry buildings and peak ground acceleration during the 2009 earthquake in Abruzzo (Italy)

The earthquake occurred on 6th April 2009 in Abruzzo has been characterized by distinctive features in terms of macro-seismic intensity and local amplifications: the damages to similar buildings located in nearby areas were often substantially different. In this paper an estimate of the peak ground acceleration (PGA) map has been performed analysing the observed damage mechanisms and using conventional tools for the seismic vulnerability assessment. The case here described concerns the area around San Pio delle Camere, located at 800 m a s.l. and 26 km far from L’Aquila (the earthquake epicentre). The zone is marked by relevant seismic vulnerability and subjected to local amplification effects due to variability of soil type. In the historic centre of San Pio delle Camere the damages were much less severe than those in the nearby Castelnuovo, which is only 2.5 km far and where almost complete destruction occurred even in presence of similar poor masonry building types. The trigger acceleration of the recognised damage mechanisms for every building not collapsed has been interpreted as the anchorage value attained by the local PGA. Using the seismic vulnerability assessment tools, the capacity acceleration calculated for the buildings that were completely destructed may represent the minimum value attained by the local PGA. The PGA was also deduced using the attenuation law, on the basis of actual values recorded by some accelerometric stations in the overall zone around the epicentre. Finally, the critical comparison among all results allows to appreciate also the extent of the site effects.