An energy-duration procedure for rapid determination of earthquake magnitude and tsunamigenic potential

We introduce a rapid and robust, energy-duration procedure, based on the Haskell, extended-source model, to obtain an earthquake moment and a moment magnitude, M-ED. Using seismograms at teleseismic distances (30 degrees-90 degrees), this procedure combines radiated seismic energy measures on the P to S interval of broadband signals and source duration measures on high-frequency, P-wave signals. The M-ED energy-duration magnitude is scaled to correspond to the Global Centroid-Moment Tensor (CMT) moment-magnitude, M-w(CMT), and can be calculated within about 20 min or less after origin time (OT). The measured energy and duration values also provide the energy-to-moment ratio, Theta, used for identification of tsunami earthquakes. The M-ED magnitudes for a set of recent, large earthquakes match closely M-w(CMT), even for the largest, great earthquakes; these results imply that the M-ED measure is accurate and does not saturate. After the 2004 December 26 Sumatra-Andaman mega-thrust earthquake, magnitude estimates available within 1 hr of OT ranged from M = 8.0 to 8.5, the CMT magnitude, available about 3 hr after OT, was M-w(CMT) = 9.0, and, several months after the event, M-w = 9.1-9.3 was obtained from analysis of the earth normal modes. The energy-duration magnitude for this event is M-ED = 9.2, a measure that is potentially available within 20 min after OT. After the 2006 July 17, Java earthquake, the magnitude was evaluated at M = 7.2 at 17 min after OT, the CMT magnitude, available about 1 hr after OT, was M-w(CMT) = 7.7; the energy-duration results for this event give M-ED = 7.8, with a very long source duration of about 160 s, and a very low Theta value, indicating a possible tsunami earthquake.