Earthquakes often happen near volcanoes, but this is not always true. The centers of some are【L1】______. The bottom of the sea s

Earthquakes often happen near volcanoes, but this is not always true. The centres of some are under the sea. The bottom of the sea suddenly moves. The powerful forces inside the earth break the rocks. The coast is shaken and great waves appear. These waves travel long distances and rush over the land when they reach it. They are strong enough to break down houses and other buildings; sometimes they break more buildings than the earthquake itself.
    Very often fires followed the most serious earthquakes. In 1906, the great earthquake at San Francisco broke the gas-pipes. The gas escaped, and soon large numbers of fires were burning in the city. The water-pipes were also shaken and broken; so it was not possible to put the fires out. There was no water. The Tokyo earthquake of 1923 happened just before the middle of the day. People were cooking meals on their fires at that time. When the ground shook, the fires shook too. Hot materials were thrown on the different parts of the houses, some of which were made of wood. Soon 134 fires were burning in the city.
    What kind of building stands up best in an earthquake? A building with concrete walls is perhaps the best. A steel frame will make it even stronger. The frame holds the different parts together, and the walls do not easily fall. There is less chance of fire because concrete and steel do not burn. The Americans carefully studied the results of the earthquake in San Francisco, and they are convinced that this kind of building is the safest.