After the occurrence of a large earthquake, rapid reporting is useful and necessary for resource dispatch management and quick damage assessment. In practice, a ground-motion prediction or a shaking-intensity estimation can be realized once the location and magnitude of an earthquake become available. Rapid availability of event information can also fulfill inquiries and alleviate the misgivings of the public and media.

Using the traditional travel-time method, rapid earthquake location is a simple task once a few P-wave arrivals are known. In contrast, a quick and accurate estimate of earthquake magnitude is a nontrivial problem, especially for an extremely large regional event. For a teleseismic-determined moment magnitude, it may take tens of minutes for the propagation of teleseismic waves. For a method using first-arrival P waveforms of broadband seismograms for moment magnitude determinations (Tsuboi et al., 1995,1999), the reporting time for moderate-sized earthquakes still takes several minutes. In addition, common high-gain broadband stations will suffer a severe amplitude-clipping problem from regional large earthquakes.

The M_w 9.0 (Global Centroid Moment Tensor [CMT]) Tohoku-Chiho Taiheiyo-Oki (Tohoku) earthquake that occurred on 11 March 2011 was unprecedented in size since Japan started modern instrumental recordings 130 years ago. The megathrust Tohoku earthquake ruptured the Pacific–North American (Okhotsk) plate boundary off the Pacific coast of northeastern Japan.

The work presented here employed the empirical method of Wu and Teng (2004) for quick M_w determinations of crustal earthquakes in Japan using time integration over the strong-shaking duration for absolute values of acceleration records.

In the study of Wu and Teng (2004), the maximum magnitude was for the 1999M_w 7.6 (Global CMT) Chi-Chi earthquake in Taiwan. In this work, the largest event was the 2011 M_w 9.0 Tohoku earthquake in Japan. We show that the method of Wu and …