Mwpd: Rapid Determination of Earthquake Magnitude and Tsunamigenic Potential from P Waveforms

We present a duration-amplitude procedure for rapid determination (within 20 minutes of OT) of earthquake moment magnitude, Mwpd, from P-wave recordings at teleseismic distances. The procedure determines apparent source durations, T0, from high-frequency, P-waveforms, and estimates moments by integration of broadband displacement waveforms over the interval tP to tP+T0, where tP is the P arrival time. Application to 79 recent, large earthquakes (Mw 6.6 to 9.3) shows that scaling of the moment estimates for interplate thrust and possibly tsunami earthquakes is necessary to best match Mw. With this scaling, Mwpd matches Mw typically within ±0.2 magnitude units and Mwpd does not saturate for the largest events. The explicit use of the source duration, the moment scaling, and other characteristics of the duration-amplitude methodology make it an extension of the widely used Mwp rapid-magnitude procedure. The obtained durations and moments allow rapid estimation of the energy-to-moment ratio Θ for identification of tsunami earthquakes.