Regional Centroid Moment Tensors


The Alpine Mediterranean region is characterized by complex active tectonics, connected to the convergence between Africa and Eurasia, but also to the motion of several microplates, producing a wide range of tectonic regimes. Earthquake focal mechanisms contribute to the understanding of the active tectonics, and in this complex region yield fundamental information.

Seismicity in the Mediterranean area is rather diffuse, and characterized by mostly moderate energy release. Moderate-magnitude events are therefore particularly important because more widely spread than the relatively infrequent larger-magnitude earthquakes. Small or moderate events are difficult to model at teleseismic distance with the classical Centroid Moment Tensor (CMT) method, owing to the low signal-to-noise ratio of the long period body waves used. The inversion of intermediate period surface waves recorded at regional distance allows instead to compute moment tensors also for these events with similar reliability as given by the standard CMT analysis.

We compute Regional Centroid Moment Tensors (RCMT) routinely since 1997 for intermediate- magnitude earthquakes (about 4.5 < M < 5.5) occurring in the Euro-Mediterranean region, and we maintain a catalog of solutions. Our catalog occasionally also lists events with magnitudes as low as 4.0, obtainable when the station distribution is particularly favorable. The catalog generally does not include larger events, which can instead be found in the global CMT Catalog maintained at Harvard.

For the 6-year period 1997-2002, 420 solutions have been obtained -- if added to the standard CMTs available for larger events for this time span and this area, we increase the total number of earthquakes with a known moment tensors by almost 300%.

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 seismograms recorded by MedNet (Mediterranean Network) stations accessible trough the web, and on data from other web distribution organisations as VEBSN-MEREDIAN system.

Read our web paper with a description of the project published on Vol.2, No.1, page 4 of the ORFEUS Electronic Newsletter.


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