Earth Planets Space, Vol. 63 (No. 7), pp. 821-826, 2011
Hiroaki Tsushima1, Kenji Hirata1, Yutaka Hayashi1, Yuichiro Tanioka2, Kazuhiro Kimura1, Shin'ichi Sakai3, Masanao Shinohara3, Toshihiko Kanazawa3, Ryota Hino4, and Kenji Maeda1
1Meteorological Research Institute, Japan Meteorological Agency, 1-1 Nagamine, Tsukuba, Ibaraki 305-0052, Japan
2Institute of Seismology and Volcanology, Hokkaido University, Kita 10 Nishi 8, Kita-ku, Sappopro 060-0810, Japan
3Earthquake Research Institute, University of Tokyo, 1-1-1, Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan
4Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku University, 6-6 Aramaki-Aza Aoba, Sendai 980-8578, Japan
(Received April 7, 2011; Revised June 29, 2011; Accepted June 30, 2011; Online published September 27, 2011)
Tsunami heights greater than 4 m were observed at several coastal tide-gauge stations during the tsunami generated by the 2011 off the Pacific coast of Tohoku Earthquake (Mw 9.0), causing thousands of casualties and damaging infrastructure along the Pacific coast of Japan. We retrospectively applied an algorithm of near-field tsunami forecasting to tsunami data that were recorded at various offshore tsunami stations 5-10 min before the tsunami reached the coastal tide-gauge stations nearest to its source. We inverted the waveform data recorded offshore to estimate the distribution of the initial sea-surface height, and then tsunami waveforms were synthesized from the estimated source to forecast tsunami arrival times and amplitudes at coastal tide-gauge stations. As a result of a retrospective application made 20 min after the earthquake, tsunamis with heights of 6-14 m were forecasted at tide-gauge stations nearest to the source where the sea-level increase due to the actual tsunami began to exceed 1 m after an elapsed time of 25 min. The result suggests a possibility that the forecasting method we used could contribute to the issuing of reliable near-field tsunami warning for Mw 9 earthquakes.
Key words: Near-field tsunami forecasting, ocean-bottom pressure gauge, GPS buoy, tsunami waveform inversion.