HR: 1340h
AN: S53A-1034    [Abstracts]
TI: M_wpd: Rapid Determination of Earthquake Magnitude and Tsunamigenic Potential from P Waveforms
AU: Lomax, A
EM: anthony@alomax.net
AF: ALomax Scientific, 161 Allee du Micocoulier, Mouans Sartoux, 06370, France
AU: * Michelini, A
EM: michelini@ingv.it
AF: Istituto Nazionale di Geofisica e Vulcanologia (INGV), Via di Vigna Murata, 605, Rome, 00143, Italy
AB: We present a duration-amplitude procedure for rapid determination of an earthquake moment magnitude, M_wpd, from P-wave recordings at teleseismic distances. The M_wpd magnitude can be obtained within 20 minutes or less after the event origin time since the required data is available in near-real time. The procedure determines apparent source durations, T₀, from high-frequency, P-wave records, and estimates moments through integration of broadband displacement waveforms over the interval t_P to t_P+T₀, where t_P is the P arrival time. We apply the duration-amplitude methodology to a number of recent, large earthquakes (Global Centroid-Moment Tensor magnitude, M_w^CMT, 6.6 to 9.3) with diverse source types. The results show that a correction to the moment estimates for interplate thrust and possibly tsunami earthquakes is necessary to best match M_w^CMT. With this correction, M_wpd matches M_w^CMT typically within ±0.2 magnitude units, with a standard deviation of σ=0.11, outperforming other approaches to rapid magnitude determination. In addition, M_wpd does not exhibit saturation for the largest events, or, equivalently, ΔM=M_wpd-M_w^CMT does not become more negative with increasing M_w^CMT. The explicit use of the source duration for integration of displacement seismograms, the moment correction, and other characteristics of the duration-amplitude methodology make it an extension of the widely used, M_wp, rapid-magnitude procedure. The obtained duration-amplitude moments and durations allow rapid estimation of the energy-to-moment ratio Θ used for identification of tsunami earthquakes. The need for a moment correction for interplate thrust and possibly tsunami earthquakes may have important implications for the source physics of these events.
UR: http://www.alomax.net/posters/duration-amplitude/
DE: 4564 Tsunamis and storm surges
DE: 7203 Body waves
DE: 7215 Earthquake source observations (1240)
DE: 7219 Seismic monitoring and test-ban treaty verification
DE: 7294 Seismic instruments and networks (0935, 3025)
SC: Seismology [S]
MN: 2007 Fall Meeting