Measurement of Earthquake Size

The paper begins with a brief review of the research history of earthquake size measurement. On this basis,the author pointed out the following points: 1 In recent decades,ML,mb( mB),MSmagnitude scales are widely used as measures of earthquake size. However,these magnitude scales have a deficiency of "overgeneralization " and"magnitude saturation". Moreover,since they do not fully take into account the regional difference of seismic attenuation, especially the difference of site effects on the amplification of ground motion,these magnitude scales are but inaccurate measures of earthquake size. 2 Seismic moment M0 not only has clear physical meaning,but also overcomes the deficiencies existing in ML,mb( mB) and MSmagnitude scales,so it is the most suitable physical quantity for measuring earthquake size scientifically. In order to continue to use the term "magnitude",Kanamori defined the moment magnitude scaleΔσ. Although its prerequisite assumptions remain to be studied,it is still a reasonable scale used as a measure of the relative size of an earthquake. 3 For measuring the earthquake size more scientifically,we must make full use of a large amount of waveform data from modern regional digital seismograph networks,strengthen the research on seismic wave attenuation characteristics,site effect,calculation of source parameters and the related scaling relations. In improving the measurement methods for ML,mb( mB) and MSmagnitude,we should focus on the improvement of MWscale and carry forward the work as gradually taking MWmagnitude scale as the uniform physical quantity to measure the relative size of earthquakes,so as to lay a more solid foundation for research in earthquake science and earthquake prediction.

The paper begins with a brief review of the research history of earthquake size measurement. On this basis, the author pointed out the following points： ① In recent decades, ML, mb （mH ）, Ms magnitude scales are widely used as measures of earthquake size. However, these magnitude scales have a deficiency of ＂overgeneralization＂ and ＂magnitude saturation＂. Moreover, since they do not fully take into account the regional difference of seismic attenuation, especially the difference of site effects on the amplification of ground motion, these magnitude scales are but inaccurate measures of earthquake size. ② Seismic moment M0 not only has clear physical meaning, but also overcomes the deficiencies existing in ML, mb （mB ） and Ms magnitude scales, so it is the most suitable physical quantity for measuring earthquake size scientifically. In order to continue to use the term ＂magnitude＂, Kanamori defined the moment magnitude scale Act. Although its prerequisite assumptions remain to be studied, it is still a reasonable scale used as a measure of the relative size of an earthquake. ③ For measuring the earthquake size more scientifically, we must make full use of a large amount of waveform data from modern regional digital seismograph networks, strengthen the research on seismic wave attenuation characteristics, site effect, calculation of source parameters and the related scaling relations. In improving the measurement methods for ML, mb （mB ） and Ms magnitude, we should focus on the improvement of Mw scale and carry forward the work as gradually taking Mw magnitude scale as the uniform physical quantity to measure the relative size of earthquakes, so as to lay a more solid foundation for research in earthquake science and earthquake prediction.