Joint Symposia » J04. Geohazard early warning systems

[J04-3] Geohazard early warning systems III

2017年8月3日(木) 13:30 〜 15:00 Intl Conf Room (301) (Kobe International Conference Center 3F, Room 301)

Chairs: Mitsuyuki Hoshiba (Meteorological Research Institute, JMA) , Hiroaki Tsushima (Meteorological Research Institute, Japan Meteorological Agency)

14:15 〜 14:30

[J04-3-04] Propagation of local undamped motion (PLUM) method and its improvement using P-phase discrimination for more rapid earthquake early warning based on wavefield-estimation approaches

Yuki Kodera (Meteorological Research Institute, Japan Meteorological Agency, Tsukuba, Japan)

Earthquake early warning methodologies based on wavefield estimation have been recently proposed by Hoshiba (2013) and Hosiba and Aoki (2015) to address technical challenges that come from point-source-model approaches such as underprediction of strong motion when large earthquakes (M>~8) occur and overprediction when multiple earthquakes simultaneously happen. The propagation of local undamped motion (PLUM) method is a simple wavefield-estimation algorithm derived from the method proposed by Hoshiba (2013). The PLUM method predicts strong motion at a target site by taking the maximum among real-time seismic intensities (Kunugi et al., 2013) observed at seismometers within 30km of the target site. A simulation of the PLUM method for the 2011 off the Pacific coast of Tohoku Earthquake (Mw 9.0) (the Tohoku-oki earthquake) showed that the PLUM method predicted accurate seismic intensities in the Kanto region, where the EEW system of the Japan Meteorological Agency (JMA) underpredicted strong motion.

The PLUM method, however, has room for improvement in rapid warning issuance since its prediction process rely only on strong motion by S phase and do not utilize P-phase information available before the S-phase arrival. We introduced a simple P-phase discriminator that uses V/H (ratio of vertical to horizontal components of acceleration) and modified the prediction process of the PLUM method. The modified method first conducts on-site prediction of S-phase strong motion for seismometers assumed to be observing P phase. After that, the modified method predicts strong motion for target sites in the same way as the original method. We applied the modified method to the Tohoku-oki earthquake and the Mj 6.5 and Mj 7.3 earthquakes in the 2016 Kumamoto earthquake sequence. Results showed that the modified method provided longer warning times by 5 s in the Tohoku-oki earthquake and 1 s in the Mj 6.5 and Mj 7.3 earthquakes, compared with the original method.