Magnitude determination of deep-focus earthquakes in and around Japan with regional velocity-amplitude data (II)

The magnitude determination scheme of the Japan Meteorological Agency (JMA) was revised in September 2003. This paper presents a formula for velocity magnitudes that underlies the revision. Depth dependence of the velocity magnitudes is determined so as to agree with JMA displacement magnitude for earthquakes shallower than 150km and with moment magnitudes for those deeper than 150km. The velocity magnitudes were consistent with the moment magnitude estimated with the F-net for earthquakes shallower than 550km. A comparison of velocity magnitudes and displacement magnitudes of earthquakes from 1977 to 2004 indicates that there is no noticeable temporal change except for a step of about +0.06 during the renovation of the JMA seismic network in 1994.