1. Procedure for issuance of Tsunami Forecast Japan Meteorological Agency (JMA) initiated tsunami forecast service for local tsunamis in 1952 with empirical method. We upgraded the forecast system to one with numerical simulation technique and database method in 1999, which is called Quantitative Tsunami Forecast System. Tsunami generation and propagation simulations were conducted for 100,000 different assumed faults in advance and their results were stored onto a database. We retrieve the most appropriate result from the database immediately after a large earthquake occurs, and assemble tsunami forecast to be issued. This method is also used for the international service to provide the nations in the Northwestern Pacific area with the Northwest Pacific Tsunami Advisory. 2. Application of the Earthquake Early Warning to Tsunami Forecast The Earthquake Early Warning (EEW) is a new service to announce the expected strong ground motion caused by earthquakes before it arrives. The EEW technique can estimate the hypocenter and magnitude very quickly, around a few seconds after an earthquake occurrence at the earliest. JMA aimed at the tsunami forecast dissemination within 3 minutes formerly, but it has become possible to shorten it by applying this technique since October 2006. The first application for the tsunami forecast was for the M6.9 Noto peninsula earthquake on 25 March 2007, and it took 2 minutes to issue tsunami forecast after the quake. The second one was for the M6.8 Chuetsu-oki earthquake on 16 July 2007 and the tsunami forecast was issued in 1 minute. 3. Incorporation of the CMT Solution into Tsunami Forecast Numerical simulation for the Quantitative Tsunami Forecast System was conducted under the assumption that all mechanisms were pure reverse faults with dip angle of 45 degree. From the viewpoint of the safety, JMA applies such conservative scenario as reverse fault generates tsunami most efficiently, considering that we cannot obtain the actual mechanism of the rupture in a very short time while tsunami forecast must be issued in a few minutes. By adopting the recent progress in the seismic data analysis, however, we have come to obtain the CMT solution in about ten minutes using the STS2 seismic waveform record. JMA began to incorporate CMT solution into the tsunami forecast operation in July 2007. Tsunami forecast once issued depending on the hypocenter location and Mjma will be upgraded if the CMT solution shows that the fault mechanism is normal or reverse and also that the Mw is larger than Mjma by 0.5 or more. On the other hand, if it is shown that the mechanism is a strike-slip fault, we can downgrade or cancel the forecast more promptly than before.
AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- 7299 General or miscellaneous