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If the crust (外壳) of the earth were not pretty solid (坚固的), it would be shaking about and moving up and down frequently (频繁地). However, there are places in the rocks of the earth's crust where it isn't strongly held together — where faults exist.Along the faults, one rock might push against another with great force.The energy is changed to vibration in the rocks, so they begin to shake and we have an earthquake!
The most famous one in North America was the San Francisco earthquake of 1906.
Seven hundred people died and property (财产) damage amounted to about $425,000,000.The greatest destruction came from the fires that followed the quake.
One of the most famous earthquakes in Europe took place in Lisbon, Portugal, in 1755. The city was destroyed and at least thirty thousand people were killed. In 1908, in Calabria and Sicily, a quake killed about seventyfive thousand people. In 1915，in central Italy, hundreds of towns and villages were damaged and thirty thousand people were killed.
Two great earthquakes that caused great damage in Asia took place in Tokyo, Japan, and in Gansu Province in China. The Tokyo quake of 1923 killed more than one hundred thousand people and destroyed the city and the city of Yokohama, too. The Chinese quake in 1920 covered more than three hundred square miles and killed about two hundred thousand people.
