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

Moment magnitude M-w 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 M-0 with virtually no limits in the frequency passband. For this reason, M-w does not become saturated even for the largest earthquakes ever recorded. M-w has been chosen in such a way that it coincides best with the previous definitions of magnitude (M-s, M-L, m(b), 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 M-wg with the aim of better reproducing the values of m(b) and M-s over their entire range and to better predict the energy E-S radiated by earthquakes. We show that there was no need to define such a new scale and that M-wg is not even optimal to achieve the goal of matching E-S.