Variable-Period Surface-Wave Magnitudes: A Rapid and Robust Estimator of Seismic Moments

Abstract

Abstract We demonstrate that surface-wave magnitudes ( M s ), measured at local, regional, and teleseismic distances, can be used as a rapid and robust estimator of seismic moment magnitude ( M w ). We used the Russell (2006) variable-period surface-wave magnitude formula, henceforth called M s (VMAX), to estimate the M s for 165 North American events with 3.2 M w M w estimated from broadband waveform modeling (Herrmann et al. , 2008) were regressed against M s (VMAX). M w can be estimated from M s (VMAX) using the relationship: M w =1.91+0.66 * M s (VMAX) for 2 M s M w [ M s (VMAX)] with respect to M w [Waveform Modeling] was approximately ±0.2 magnitude units (m.u). The residuals between M w [ M s (VMAX)] and M w [Waveform Modeling] show a significant focal mechanism effect, especially when strike-slip events are compared with other mechanisms. Validation testing of this method suggests that M s (VMAX)-predicted M w ’s can be estimated within minutes after the origin of an event and are typically within ±0.2 m.u. of the final M w [Waveform Modeling]. While M w estimated from M s (VMAX) has a slightly higher variance than waveform modeling results, it can be measured on the first short-period surface-wave observed at a local or near-regional distance seismic station after a preliminary epicentral location has been formed. Therefore, it may be used to make rapid measurements of M w , which are needed by government agencies for early warning systems.