Estimation of Moment Magnitude from Ground Motions at Regional Distances

We present a simple and robust approach to estimate moment magnitude (M) for events of M < 6 from regional seismographic observations (vertical component), recorded in the distance range from 100 to 400 km. M can be estimated from 1-Hz response spectral amplitudes for events in North America with an uncertainty (standard deviation of residuals) of < 0.2 units in most regions, using the simple relationships provided herein. Advantages of the method are that it allows for consistent estimation of M across regions, and that it provides relationships that are consistent with the predictions of a stochastic point-source model for typical regional attenuation models.