Calibration of Local Versus Moment Magnitude in Greece for the Period 1976-2015: Construction and Analysis of a Homogeneous Regional Seismicity Catalog

Local magnitude has been calculated in Greece since 1964 when the National Observatory of Athens (NOA) installed one Wood-Anderson (WA) seismograph at its headquarters. The calculation of local magnitude had been performed using analog WA records until 2007, at which time synthetic WA waveforms started being used and local magnitude was estimated as the average of values from many stations. NOA also has started to produce routine regional moment tensor solutions and moment magnitudes since 2001 until the present day, while moment magnitudes from 1976 to 2000 for Greek earthquakes were only available through Global CMT (GCMT) solutions. In this proposal it is suggested to investigate the relationship between the two magnitude scales for the purpose of producing a homogeneous, with respect to magnitude, seismicity catalog for the Greek region. The calibration of local magnitude versus moment magnitude will be performed for three periods: (a) 1976-2000 for GCMT moment magnitudes, (b) 2001-2007 for NOA moment magnitudes, and (c) 2008-present for NOA moment magnitudes versus local magnitudes from synthetic WA waveforms. General Orthogonal Regression (GOR) will be used in order to find the linear relationship between the two magnitude scales, as this methodology has been shown in previous studies to provide more accurate results than standard least-squares. Using these relationships the local magnitudes will be converted to equivalent moment magnitudes and a regional seismicity catalog for the period 1976-2015 will be constructed. The new, homogeneous catalog will then be analyzed for its completeness and for temporal/spatial variations of b-values in an effort to understand better seismicity rates and improve seismic hazard estimates in the Greek region.