Comment on “A Seismic Moment Magnitude Scale” by Ranjit Das, Mukat Lal Sharma, Hans Raj Wason, Deepankar Choudhury, and Gabriel Gonzalez

Abstract

ABSTRACT Moment magnitude Mw was first defined by Hiroo Kanamori in the late 1970s, when the availability of new force balance seismometers made it possible to measure the seismic moment M0 with virtually no limits in the frequency passband. For this reason, Mw does not become saturated even for the largest earthquakes ever recorded. Mw has been chosen in such a way that it coincides best with the previous definitions of magnitude (Ms, ML, mb, etc.) on certain ranges of values but can deviate significantly from them within other ranges. A few years ago, Das and colleagues proposed a new moment magnitude scale Mwg with the aim of better reproducing the values of mb and Ms over their entire range and to better predict the energy ES radiated by earthquakes. We show that there was no need to define such a new scale and that Mwg is not even optimal to achieve the goal of matching ES.