- © 2009 by the Seismological Society of America
We assess the use and reliability of a source inversion of the W-phase in real-time operations at the U.S. Geological Survey National Earthquake Information Center. The three-stage inversion algorithm produces rapid and reliable estimates of moment magnitude and source mechanism for events larger than Mw 7.0 within 25 minutes of the earthquake origin time, often less, and holds great promise for vastly improving our response times to such earthquakes worldwide. The method also produces stable results (within ±0.2 units of Global Centroid Moment Tensor project estimates) for earthquakes as small as Mw 5.8 when using stations out to distances of 90°. These applications extend the use of W-phase far beyond the higher magnitude events for which the inversion was originally intended, facilitating its use as a complementary approach to traditional body- and surface-wave methods for assessing the source properties of an earthquake.
Kanamori and Rivera (2008) introduced the use of W-phase as a reliable method to rapidly assess the source properties (Mw and mechanism) of earthquakes greater than ∼Mw 7.5. They showed that the W-phase inversion method has important real-time applications for tsunami warning purposes (and indeed for the calculation of earthquake moment), particularly for very large earthquakes such as the 2004 Sumatra–Andaman Islands event for which traditional methods may suffer due to the clipping of seismograms and/or because they do not deliver accurate results quickly enough to be useful for tsunami warning.
The U.S. Geological Survey (USGS) National Earthquake Information Center (NEIC) began implementation of W-phase inversion in real-time operations for testing purposes in July 2008. Here we assess the performance of this method in real time and show that W-phase not only provides rapid and accurate results for large earthquakes but also that this inversion can be …