European–Mediterranean regional centroid-moment tensors: 1997–2000

The Mediterranean region is seismically very active and undergoing rapid deformation. Earthquakes as strong as M≥6 are present, but relatively rare. On the other hand, moderate-magnitude seismicity (4.5<M<5.5) is widespread and, often, damaging. An improved knowedge of moderate-magnitude earthquakes can contribute significantly to a better understanding of active tectonics in the region. Harvard centroid-moment tensors (CMT) today represent the most widely used reference for reliable source mechanisms, but modelling seismic sources with the CMT technique for earthquakes with magnitude less than M≈5–5.5 is quite difficult. Since 1997, we are using an extension of the standard CMT algorithm to compute regional centroid-moment tensors (RCMT) for moderate-magnitude earthquakes (MW as low as 4.0), analyzing intermediate-period surface waves from regional and teleseismic seismograms. We routinely apply the algorithm to European–Mediterranean seismicity to produce a catalog of seismic moment tensors for events with magnitude between 4.5 and 5.5, which generally are not included in the Harvard CMT catalog. In this paper, we show the results for earthquakes that occurred between 1997 and 2000, consisting of 252 solutions, and we discuss the characteristics of the catalog and the areas where these new data are most relevant.