[J04-3] Geohazard early warning systems III

[J04-3-05] Recent advances in tsunami warning and earthquake early warning of the Japan Meteorological Agency after the 2011 Great Tohoku Earthquake and Tsunami

^○​Satoshi ​Harada (Japan Meteorological Agency, Tokyo, Japan)

invited

The Japan Meteorological Agency (JMA) is the sole organization to issue warnings on natural hazards in Japan. JMA started its operation of tsunami warnings in 1949 and since then JMA has improved its warnings in accuracy and swiftness. And JMA started the service of earthquake early warning (EEW) provision to the public in 2007. For the 2011 Great Tohoku Earthquake and Tsunami (Mw9.0), JMA issued Major Tsunami Warnings, the highest category of JMA's tsunami warning, in three minutes, and issued EEWs 8.6 seconds after the earthquake detection. These warnings were promptly disseminated to the public via various ways such as TV, radio and mobile phones. On the other hand, this event also posed several issues to be improved on JMA's warning systems, and JMA took various measures based on the lessons learned from this event. Major countermeasures for tsunami warnings are, 1) introduction of qualitative expression of tsunami height estimation like "Huge", which will be used when JMA issues tsunami warnings based on pre-assumed maximum magnitude because the earthquake is too large to estimate the magnitude appropriately within around three minutes, and 2) utilization of ocean bottom pressure gauges in updating tsunami warnings. Regarding EEW, as the countermeasure for the difficulty in hypocenter and magnitude estimation when multiple events occur simultaneously, JMA introduced the Integrated Particle Filter (IPF) method in 2016, which is expected to greatly improve the ability to separate individual events from simultaneously occurred multiple earthquakes. JMA also plans to introduce the new method, i.e., the propagation of local undamped motion (PLUM) method, into EEW in the near future which addresses the issue of under-prediction for massive earthquakes with large rupture zones. This method adopts the technique of sequential prediction of seismic intensity by assimilating expanding ground tremor observations into forecasting.