Uncertainties in the estimation of earthquake magnitudes in Greece

Abstract

Instrumental magnitudes in Greece have been reported as: a) M magnitudes based on the records of the Wiechert or Mainka seismographs, b) MLGR magnitudes based on the records of the Wood-Anderson (WA) seismographs (To = 0.8 sec, Veffective ∼ 1000) or other short period seismographs calibrated against WA records and, c) MLSM magnitudes based on strong motion records (accelerograms). Comparison of such magnitudes with moment magnitudes, Mw, for 329 earthquakes, with epicenters in the broader Aegean area, performed in this study, showed that M, MLGR+0.5 and MLSM are practically equal to Mw, with a small overall standard error (σ = 0.23). Therefore, equivalent moment magnitudes, Mw ∗ , estimated from these magnitudes and reported in the catalogues of the Geophysical Laboratory of the University of Thessaloniki are equal to moment magnitudes for all practical purposes with reasonable uncertainties. It has been further shown that surface wave magnitudes, Ms ,f or M s<6.0, can be also transferred into moment magnitudes, Mw ∗ , but the larger uncertainties encountered make its use rather