Local variability of the ground shaking during the 2009 L’Aquila earthquake (April 6, 2009—Mw 6.3): the case study of Onna and Monticchio villages

Abstract

The 2009 Mw 6.3 L'Aquila event caused extensive damage in the city of L'Aquila and in some small towns in its vicinity. The most severe damage was recognized SE of L'Aquila town along the Aterno river valley. Although building vulnerability and near-source effects are strongly responsible for the high level of destruction, site effects have been invoked to explain the damage heterogeneities and the similarities between the 2009 macroseismic field with the intensities of historical earthquakes. The small village of Onna is settled on quaternary alluvium and suffered during the L'Aquila event an extremely heavy damage in the masonry structures with intensity IX-X on the Mercalli-Cancani-Sieberg (MCS) scale. The village of Monticchio, far less than 1.3 km from Onna, is mostly situated on Mesozoic limestone and suffered a smaller level of damaging (VI MCS). In the present paper, we analyze the aftershock recordings at seismic stations deployed in a small area of the middle-Aterno valley including Onna and Monticchio. The aim is to investigate local amplification effects caused by the near-surface geology. Because the seismological stations are 123 784 Bull Earthquake Eng (2011) 9:783-807 close together, vulnerability and near-source effects are assumed to be constant. The waveform analysis shows that the ground motion at Onna is systematically characterized by large high-frequency content. The frequency resonance is varying from 2 to 3 Hz and it is related to alluvial sediments with a thickness of about 40 m that overlay a stiffer Pleistocene substrate. The ground motion recordings of Onna are well reproduced by the predictive equation for the Italian territory.

The 2009 April 6, Mw 6.3, L’Aquila (central Italy) earthquake: finite-fault effects on intensity data

“…2011). A well‐known case is given by the settlements of ‘Onna’ ( I = 9.5) and ‘Monticchio’ ( I = 5) in the Middle Aterno Valley, distant less than 2 km each other, located on lacustrine sediments and rock, respectively (Di Giulio et al . 2011).…”

“…Nonetheless, the differences in the local site conditions seem to have played an important role in the damage occurred at specific sites (Ameri et al 2011;Bergamaschi et al 2011). A well-known case is given by the settlements of 'Onna' (I = 9.5) and 'Monticchio' (I = 5) in the Middle Aterno Valley, distant less than 2 km each other, located on lacustrine sediments and rock, respectively (Di Giulio et al 2011). Evidence of local amplification can be found also very close to the epicentre, where the historical centre of 'Poggio di Roio' (I = 8.5), located on the Roio Basin, was completely destroyed and the neighbouring municipalities suffered very high damage.…”