- © 2009 by the Seismological Society of America
The conventional methods for rapid determination of earthquake magnitude are based mainly on peak-to-peak amplitudes of specific phases on a seismic trace. Today, broadband digital records are readily accessible in real time, enabling the use of more information from a seismogram for rapid magnitude calculation.
The aim of this work is to introduce a new magnitude scale for routine seismological analysis, denoted ME (P-wave, S-wave+coda, or both). This magnitude scale uses the signal energy and is illustrated here with a case study from southern Ontario/western Quebec (Canada). Traditional types of magnitude scales, based on the estimated maximum velocity (mb) and Richter local magnitude (ML), as well as the moment magnitude (MW), and some other magnitude types, based on the coda energy (MCoda) and envelope area (MEnv) are also computed for the study area for comparative purposes. The proposed approach employed for this study can be easily applied to any other region of the world.
The developed automatic procedure allowed the simultaneous computation of different magnitudes and different trace components and types of waves. The data used for this research are from 238 well-recorded earthquakes between 1991 and 2006 in southern Ontario/western Quebec/northern Ohio/northern NY State (1.0 < mN < 5.5).
The results of our work show that, in general, magnitude values based on signal energy ME give less scattered estimates than magnitude values based on peak-to-peak measurements. We recommend using ME (S + coda) scale (vertical component) for quantifying the earthquakes in the study area in the future. The magnitude formula for this scale is given by ME = 0.5log ẼS + 0.92logD + 3.56 + S, where ẼS is the signal energy defined here (Ζv2s Δt, vS is measured in mm/s, Δt is the sample interval in seconds), D is the epicentral distance in km, and S is the station correction. The new ME magnitude can be used for a quick estimate of the MW magnitude for the study region using the relationship: MW = ME – 0.51 (for earthquakes with ME ≥ 2.6), obtained here.