Variable-period surface-wave magnitudes; a rapid and robust estimator of seismic moments

We demonstrate that surface-wave magnitudes (M (sub s) ), measured at local, regional, and teleseismic distances, can be used as a rapid and robust estimator of seismic moment magnitude (M (sub w) ). We used the Russell (2006) variable-period surface-wave magnitude formula, henceforth called M (sub s) (VMAX), to estimate the M (sub s) for 165 North American events with 3.2<M (sub w) <6.5 at distances ranging from 48 to 5268 km. Of the 7370 event-station pairs, more than half (4051) of the measurements were at distances less than 1000 km. M (sub w) estimated from broadband waveform modeling (Herrmann et al., 2008) were regressed against M (sub s) (VMAX). M (sub w) can be estimated from M (sub s) (VMAX) using the relationship: M (sub w) =1.91+0.66 (super *) M (sub s) (VMAX) for 2<M (sub s) <6. The observed scatter of the M (sub w) [M (sub s) (VMAX)] with respect to M (sub w) [Waveform Modeling] was approximately + or -0.2 magnitude units (m.u). The residuals between M (sub w) [M (sub s) (VMAX)] and M (sub 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 (sub s) (VMAX)-predicted M (sub w) 's can be estimated within minutes after the origin of an event and are typically within + or -0.2 m.u. of the final M (sub w) [Waveform Modeling]. While M (sub w) estimated from M (sub 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 (sub w) , which are needed by government agencies for early warning systems.