We determined the centroids and stopping point of the high frequency energy radiation (HFER) of the 2003 Tokachi-Oki earthquake (Mw 8.1). We used tele-seismic data and basically followed the procedure of Gusev et al. (2007), who used the empirical Green’s functions (EGFs) technique. We first chose several small events that occurred in the nearby region of the source. The waveform data were retrieved from the Data Management Center of the IRIS. We calculated correlation among their smoothed envelopes in the frequency bands, 0.4-1.2 Hz, 1.2-2.0 Hz, 2.0-3.0 Hz, and 3.0-4.0 Hz to obtain suitable EGFs. We calculated envelopes of the P-wave waveforms of the main shock and EGFs in the above four frequency bands, and smoothed them. Then, we performed deconvolution of the smoothed envelopes of the main shock using those of EGFs to obtain the HFER signals in each band for each station. A non negative constraint was applied to this calculation. Finally, we calculated the times and locations of the centroids and the stopping point of the HFER.
The obtained centroids of the HFER are consistent with those obtained by previous studies using different data sets and methods. The centroid times and source time are well constrained, while constraint for the centoid locations and stopping point are relatively weak.
Our results show that this method is applicable to determination of centroids of HFER of large earthquakes for which strong motion data is not available. One of the advantages of this method is that it is possible to obtain good azimuth coverage using tele-seismic waveform data.