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High frequency analysis
3/11/2011 (Mw 9.0), Tohoku-oki, Japan

Risheng Chu and Don Helmberger (Caltech).

Data selection and processing

We used teleseismic waveforms recorded by global broadband seismic stations at distances between 30 and 90 degrees. 288 out of 376 stations have good high-frequency signals. All seismograms are bandpass-filtered at 2~4 Hz to investigate the radiation of the 2011 Tohoku-oki earthquake. There is some directivity with the shortest duration near 260 degrees where the finite fault models have the strongest teleseismic observations. These results suggest predominantly bilateral rupture with concentrated source dimension with slow rupture velocity. See Ni et al. (2005) for a comparison with the Great Sumatra earthquake.


Figure 1: Averaged source duration of the main shock as a function of azimuth. Colorbar indicates count of rays used in each azimuth of 30 degrees. Radius of each direction represents source duration with a step of 22 sec. The shortest and longest durations are in the southwestern and northeastern direction, respectively.

Figure 2: Typical smoothed envelopes (2~4 Hz bandpassed). Red dots represent 90% energy cutoff in a time window of 250 sec. Station names are given behind each trace.


Ni, S., H. Kanamori, and D. V. Helmberger, Energy radiation from the Sumatra earthquake, Nature, 434, pp. 582, 2005.

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