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Istituto Nazionale di Geofisica e Vulcanologia MedNet

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Regional Centroid Moment Tensors.
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Regional Centroid Moment Tensors (RCMTs) the Mediterranean

Fast earthquake source mechanism

Earthquake focal mechanisms can contribute considerably to the understanding of the active tectonics. The Centroid Moment Tensor (CMT) method has shown to be one of the most robust and reliable ways for computing focal mechanisms.

The Alpine Mediterranean region is characterized by a complex active tectonics, connected to the convergent motion between Africa and Eurasia, but also to the motion of several microplates, producing a wide range of tectonic regimes. Seismicity is rather diffuse, and characterized by mostly moderate energy release.

In the Mediterranean area, moderate-energy (4.5 < M < 5.5) seismicity is particularly important because it is widely spread, and more common than the relatively infrequent larger-magnitude events. Small or moderate earthquakes are impossible to model at teleseismic distance with the classical CMT method, owing to the low signal to noise ratio of the long period body waves used.

The surface wave Regional Centroid Moment Tensor calculation is very fast, allowing rapid determination of source mechanisms, a feature of great importance for scientific and relief operations following an earthquake (Ekström et al., 1998) . For the fast determination, we rely on data recorded at MedNet (Mediterranean Network) stations accessible by telephone dial-up or the Internet. Long period seismograms are automatically extracted in nearly-real time by the MUSCLES system (Mednet Unmanned Stations CalLer for Extraction of  Seismograms), by calling MedNet stations in the occurrence of a seismic event (Mazza et al., 1998).