The April 2009 L’Aquila earthquake: recordings in the Colosseum area

First 3D seismic array realized in the city of Rome. It recorded the mainshock and moderate-magnitude aftershocks of the 6 April 2009 M 6.3 L’Aquila seismic sequence, about 90 km northeast of Rome, provided the first earthquake ground-motion recordings in the urban area of Rome. Such recordings offer an unprecedented opportunity to calibrate the city response to central Apennine earthquakes—earthquakes that have been responsible for the largest damage to Rome in historical times. Let’s note the difference in amplitute and duration of the soil shaking on the surface in respect of the bottom of the main sedimentary body of the city: the Tiber valley.

INGV Colosseo Stations C2 C1 C3 C4 C5 C6 6 portable seismic stations has been installed inside the Colosseo for un unprecedent

32 m Stern wall Valadier wall Valadier wall was reconstructed by Giuseppe Valadier in 1852 under Pio IX P.M.

Funiciello et al., 1995 View of the near-surface Geology of the Colosseo area

Funiciello et al. 1995

Numerical simulation of the soil shaking along a 2D vertical section crossing the Colosseo. Look, in the stacking of the synthetics, at the differences in amplification and duration of the soil shaking within the sedimentary basin underlying the Valadier wall. Let us see better the dynamics in the movie

Moczo et al., (1995); Caserta (1998)

Is 1.2 Hz a resonance frequency? To check this we used a monochromatic plane-wave

To check the role played by the basin we installed two stations in the Ipogei

Valadier wall Stern wall Receiver function aftershok Mw 4.2 Even if a shift in frequency takes place, the differences in amplitude are not enough to identify an amplification of the soil shaking in the valley Frequency (Hz)

Valadier wall Stern wall The filtered signals do not show an amplification one in respect of the other, actaully

Outcropping Geological Formations: Bedrock: Plio-Pleistocene clay Pleistocene tuffs (Vulcanites) Holocene alluvium Bindi et al. (2008)Di Alessandro et al. (2008) Caserta et al., (2013) On the other hand, the Peack Ground Velocity values are in agreement with regression curves according with Magnitude and epicentral distance

Valadier wall Stern wall PS ~10% S Coda at t~40s an abrupt change in the derivative takes place The array intensity shows a difference of 10% in absorbed energy between the two sides of the Colosseo; it is too small to conclude that the valley is able to amplify the shaking. As a consequence is hard to state the Valadier wall has been damaged by differential motions

In order to see how such energy is transmitted to the higer floors we installed first a third station at the ground level Stern wall

Valadier wall Stern wall Ground level Receiver function aftershok Mw 4.2 This show how the foundations de-amplify the shaking

Valadier wall Stern wall Ground level This is confirmed by the filtered signals

Valadier wall Stern wall Ground level ~25% In fact, the Valadier wall absorbs 35% more energy than the ground level

What happens at the first floor? Stern wall

Ground level First level ~6 times At the first floor the absorbed energy is 6 times more than at the ground level

Ground level First level Receiver function aftershok Mw 3.5 Two frequency bands are interested in the energy transfer process: 1 – 2 HZ and 4 -6 Hz Let start with the first frequency band

Ground level First level

Stern wall Ground level First level First level filt. Through the first frequency band passes ~ 50% of the total energy absorbed by the first floor

Ground level First level

Stern wall Ground level First level First level 1-3Hz First level 4-6Hz The absorbed energy in the second frequency band is equal to the Ground level

Concluding Remarks The Fosso Labicano valley seems to play no role in amplifying the soil shaking; the foundations seems to ‘filter’ the seismic input radiation; the absorbed energy is transmitted to the first level mainly through the resonance frequency