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The 2001 Savuto Valley (Calabria) earthquake: the relevance of the minor seismicity
by
Ignazio Guerra
Calabria University, Dept. of Physics
Coauthors: M.R. Gallipoli, A. Gervasi, P. Harabaglia and M. Mucciarelli
On October 18, 2001 an earthquake with magnitude mL = 4.2 hit the area that separates the Upper Crati and Savuto Valleys at about 15 km to the East - South East of Cosenza (northern Calabria),. In some villages seismic intensities attained an intensity attributable to the degree VII MCS. The main shock was followed by a sequence of about ninety events, that lasted about a month.
Despite its low energy level, there are several reasons that make it noteworthy. The first one is the relative seismic quiet that characterises Calabria since 1908, after the terrific series of earthquakes happened in the preceding 125 years: standing this situation, each low energy earthquake has to be considered as an irreplaceable source of useful information about the space distribution of tectonically active structures and about any other feature relevant for the seismic hazard assessment, like, for example, the site attenuation/amplification effects.
The second reason is the possibility to investigate the geodynamical context within which the event takes place. In particular, from the microseismic point of view, the 2001 earthquake evidences an interesting migration of the stress release from a NW-SE trending tectonic structure to a second one, parallel to the first and displaced about 10 km North-Eastward.
From the macroseismic point of view, the 2001 mesoseismal area coincides with that of the 1870 earthquake, that attained a X MCS maximum. Assuming a substantial linearity in eventual site effects, this makes the 2001 event a good sized-down example of what should happen in case of repetition of a large event such as that of 1870.
A further noticeable feature of the 2001 seismic event is the clear separation between the location of the main shock (and the denser cluster of aftershocks) and the area that undergone heaviest levels of damagement, pointing to dangerous site amplification effects. Instrumental measurements have shown a good correlation between the local seismic response, evaluated trough the HVSR (Nakamura’s technique), and the permanent effects observed inside the most damaged town.
Date received: September 13, 2004
Copyright © 2004 by the author(s). The author(s) of this document and the organizers of the conference have granted their consent to include this abstract in Atlas Conferences Inc. Document # caon-50.