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[STT40-P02] Detection of aftershocks of the 2004 Niigata-Chuetsu earthquake using single-station matched filter technique
Keywords:Niigata-Chuetsu earthquake, Aftershocks
The detection of aftershocks immediately after the occurrence of a large earthquake plays an important role in forecasting subsequent aftershocks. It has been well known that the 2004 Niigata-Chuetsu earthquake (Magnitude 6.8, 23 Oct. 2004) (also called as Mid-Niigata prefecture earthquake)has more intensive and longer aftershock sequence than other recent inland earthquakes with the similar magnitude. However, immediately after the mainshock rupture, an incompleteness of aftershock catalog has been reported by previous studies (Enescu et al., 2007; Morikawa et al., 2021), due to an overlapping arrivals of waveforms from the intensive aftershocks and a lack of waveform data caused by power outages. Therefore, we attempted to detect immediate aftershocks following the mainshock rupture applying a new matched filter method using a only single station (Kurihara et al., 2021), which calculates the product of mutual information and correlation coefficient as an index, to continuous waveform data nearby the mainshock hypocenter.
We used one-day continuous waveform data retrieved at the N. TDMH (Tadami, Fukushima Prefecture) station (Hi-net) on the mainshock occurrence (October 23, 2004), which was not affected by the power outage. As template earthquakes for the matched filter technique, we used a total of 9884 events occurred in 2004 in and around the aftershock area. We used the frequency band of 4–12 Hz and the time window length of 3 seconds. As a result, we detected about 2400 earthquakes. The lower limit of the magnitude of the detected earthquakes tends to decrease gradually in the first few hours after the mainshock. Because of this tendency, the number of detected earthquakes linearly increases (~300 events/hr) for about 6 hours after the occurrence of the mainshock. However, the Omori law, in which the number of aftershocks gradually decreases with elapsed time, was confirmed if we applied the cutoff of magnitude.
We used one-day continuous waveform data retrieved at the N. TDMH (Tadami, Fukushima Prefecture) station (Hi-net) on the mainshock occurrence (October 23, 2004), which was not affected by the power outage. As template earthquakes for the matched filter technique, we used a total of 9884 events occurred in 2004 in and around the aftershock area. We used the frequency band of 4–12 Hz and the time window length of 3 seconds. As a result, we detected about 2400 earthquakes. The lower limit of the magnitude of the detected earthquakes tends to decrease gradually in the first few hours after the mainshock. Because of this tendency, the number of detected earthquakes linearly increases (~300 events/hr) for about 6 hours after the occurrence of the mainshock. However, the Omori law, in which the number of aftershocks gradually decreases with elapsed time, was confirmed if we applied the cutoff of magnitude.