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Centro di Ricerche Sismologiche

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The Lunigiana earthquake and its effects in Northern Italy

21 June 2013

 

 

The earthquake of June 21 at 12:34 pm in Lunigiana had a very strong resentment in Northern Italy and in particular in the Northeast.

This effect depends not only on the directivity of the source, i.e  from the direction of propagation of seismic waves from the hypocenter to a receiver, but also from the so-called focal mechanism, namely the description of the stress and the source of the fault plane that has moved.

In this case, the focal mechanism determined by OGS  shows that the orientation of the fault is East-West, quite unusual for earthquakes in this area which usually are oriented NW-SE

However in  the northeast were added two other factors: the amplification of the waves due to soft sediments and the sum of direct waves with those travelling deep into the crust and that are refracted toward the surface by the discontinuity of Mohorovic. This explains why the local magnitude of the OGS is greater than that of INGV that instead uses a greater number of stations better distributed around the epicenter.

The OGS moment magnitude is equal to 5.3, in agreement with the estimates of moment magnitude of other monitoring centres.