Moment magnitude estimates for earthquakes in the Greek region: A comprehensive comparison

Many different agencies and research groups routinely estimate moment magnitudes (M_w) in the Mediterranean area as a means of offering an unbiased quantitative assessment of earthquake size. In this work, a comprehensive comparison is undertaken of the moment magnitudes estimated for earthquakes in the Greek region by the Global Centroid Moment Tensor (Global CMT) group, Regional CMT group, the Swiss seismological service based in ETH Zürich, Aristotle University of Thessaloniki (AUTH), and the National Observatory of Athens (NOA) Institute of Geodynamics. The orthogonal regression method is applied to obtain the best-fit line between the NOA and the other magnitude estimates. Results show that NOA moment magnitudes are, on average, smaller than Global CMT/Regional CMT/ETH magnitudes by about 0.12–0.19 magnitude units, whereas they agree quite well with AUTH magnitudes. It is also shown that for the calibration of NOA magnitudes relative to the other magnitude estimates, no scaling correction is needed, but only a variable offset correction should be applied. Taking advantage of the fact that Global CMT and Regional CMT magnitudes are fully compatible, it is possible to calibrate NOA magnitudes relative to Global CMT and then merge the moment magnitudes of the three databases. The new catalog compiled in this way is homogeneous with respect to Mw and includes 1966 earthquakes spanning a period from 1976 to 2014.