A large proportion of the tsunami warnings issued by the Pacific Tsunami Warning Center (PTWC) were never realized (Bernard 1998). For tsunami warning, the earthquake magnitude and location alone are clearly not enough, especially for so-called tsunami earthquakes (Kanamori 1972) that produce tsunamis larger than might be expected from the high-frequency content of the seismic signal of the earthquake. Additional information on the earthquake source and seismic signals may help to reveal the tsunamigenic nature of such events. The mechanism of tsunami earthquakes was explained by Kanamori in 1972. He studied 5–100-s period seismic waves of...

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