Because of the expense and time needed for the construction projects described above, the most practical and effective way to save lives is an early warning system. The Japan Meteorological Agency introduced a quantitative tsunami forecast system in April 1999. The system simulates about 100,000 tsunami patterns, all based on hypothesized earthquakes of differing intensities, with epicenters of varying depths located at 4,000 places along faults off Japan's shores. Calculations were made for the expected heights and arrival times of tsunamis after possible seismic activity at any of these epicenters, and the results of these calculations were made part of a database. If a jolt occurs, the database is searched for predicted values that most closely match the location, depth and intensity, making it possible to issue a warning just three to five minutes after a quake. If the estimated maximum possible risk is great enough, people are told to evacuate even when it is not sure a tsunami will hit.

But a lapse of three minutes between earthquake and warning is too long for a tsunami like the fast-striking one that pounded Okushiri Island. The Japan Meteorological Agency has therefore begun work on a more advanced system with a new type of seismograph that can forecast a tsunami within two minutes of seismic activity. When an earthquake occurs, conventional seismographs record the arrival of faster moving compressional (P, or primary) waves and slower moving shear (S, or secondary) waves, and this time lag is used to determine the epicenter location. With the new type of seismograph, however, the location is calculated using only the initial wave pattern of the P waves. This means that the epicenter can be located a mere 30 seconds after the jolt. Then the quantitative forecast system swings into action, making it possible to issue a warning within just two minutes of the quake.

The Agency plans to have finished installing these new seismographs in 203 locations throughout Japan by 2006, and has already begun test operations. If the new system permits accurate forecasts, it can be used to issue warnings less than two minutes after seismic activity, making it the most advanced in the world.

At the end of March 2005, Japan's quantitative tsunami forecast system extended its range to the Pacific Ocean between the Philippines and Indonesia, and is now providing information for forecast purposes. Plans call for the range to be extended soon to the Yellow Sea and areas off the coast of Malaysia. The Agency has also decided to develop a system based on earthquake intensity calculations, to provide information on possible tsunamis in the Indian Ocean.

Year

Tsunami name / No. killed and missing / Height

1771

Yaeyama Earthquake and Tsunami / Approx. 12,000 people / Giant tsunami

1854

Ansei Tokai Earthquake, Nankai Earthquake / 2,000 - 3,000 people / Giant tsunami

1896

Meiji Sanriku Earthquake and Tsunami / Approx. 22,000 people / 24.4 m

1933

Showa Sanriku Earthquake and Tsunami / Approx. 3,000 people / 28.7 m

1944

Showa Tonankai Earthquake / Approx. 1,200 people / 10 m

1946

Showa Nankai Earthquake / Approx. 1,400 people / 4 - 6 m

1960

Chilean Earthquake and Tsunami / Approx. 140 people / 5 - 6 m

1968

Tokachi-oki Earthquake / Approx. 50 people / 3 - 5 m

1983

Nihonkai Chubu Earthquake / Approx. 100 people / More than 6 m

1993

Hokkaido Nansei-oki Earthquake / Approx. 230 people / 29 m