Tsunami is greatly shaken by the earthquake. Thus, the wavelength would become several tens of kilometers to several hundreds of kilometers.
Even if the water depth is about 1000 meters, due to a long wavelength, it becomes shallow for the tsunami.
For waves of long wavelengths more than water depth, the wave velocity is determined by the depth regardless of the wavelength.
For 1000-meter depth, the velocity of a tsunami reaches 360 kilometers per hour (224 miles per hour).
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