听力原文：A tidal wave is a very large and very destructive wall of water that rushes in from the ocean toward the shore. Many scientists call these huge waves tsunami. In Japanese tsunami means 'storm wave'. But do you know that tidal waves are not caused by storms and that they are not true tides at all? A true tide is the regular rise and fall of ocean waters, at definite times each day, but a tidal wave comes rushing in suddenly and unexpectedly. A tidal wave is caused by an underwater earthquake. Scientists call an underwater earthquake a seaquake. The word' seaquake' is made up of two words, the word' sea' which means' ocean' and the word' quake'. 'To quake' means' to shake' or 'to tremble'. When a seaquake takes place at the bottom of the ocean, the ocean floor shakes and trembles, and sometimes the ocean floor shifts. It is this shifting that produces the tidal wave. The tidal wave begins to move across the sea at great speed. Tidal waves have taken many human lives in the past. Today scientists can predict when a tidal wave will hit land. They use a seismograph to do this. A seismograph is an instrument that records the strength, the direction, and the length of time of an earthquake or seaquake. It is not possible to hold back a tidal wave, but it is possible to warn people that a tidal wave is coming. This warning can save many lives. What does the Japanese word 'tsunami' mean?