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April 18, 1906, California's San Andreas Fault snaps, shaking San Francisco for nearly 60 terrifying seconds .When the trembling stops, the disaster is only beginning.
Gas lines rupture1, setting off massive fires, some 700 people die. Most of the city is reduced to ruins. This trembling of the ground caused when masses of rocks suddenly shift below the Earth’s surface is called an earthquake.
Hundreds of little earthquakes shake the planet every day, but most pass unnoticed. They usually occur along the boundaries of the thin plates that cover the Earth like an egg shell. Driven by the heat deep within the Earth’s core, the plates grind against each other along lines called faults. When a plate’s motion is blocked, stress builds up. Finally the fault gives way. The released energy raises through the Earth in the form of seismic2 waves .Scientists record these waves on a device called a seismograph.These zigzag3 lines show the strength of various seismic waves. Using the line, scientists grade the earthquakes on the Richter scale. For a quake to measure one number higher on the Richter scale, it must release about 30 times as much energy as the number below it.
Every year about 100,000 earthquakes rumble4 through the ground hard enough for people to feel them. Of these, only about 1,000 are strong enough to damage property. But a powerful earthquake can be devastating5. On average, about 10,000 people die each year as a result of earthquakes .The greatest recorded earthquake ever to hit North America measured a massive 9.2 .The tremor6 struck Alaska on March 28, 1964. A camera onboard a ship docked in Valdez recorded the draining of the entire harbor as a chasm7 opened up on the seafloor.
There is no stopping the surface of the Earth from changing and moving, so engineers are focusing on ways to create better buildings, highways and bridges, structures that will remain safe and stay in one piece the next time the Earth begins to shake.
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1 rupture | |
n.破裂;(关系的)决裂;v.(使)破裂 | |
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2 seismic | |
a.地震的,地震强度的 | |
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3 zigzag | |
n.曲折,之字形;adj.曲折的,锯齿形的;adv.曲折地,成锯齿形地;vt.使曲折;vi.曲折前行 | |
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4 rumble | |
n.隆隆声;吵嚷;v.隆隆响;低沉地说 | |
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5 devastating | |
adj.毁灭性的,令人震惊的,强有力的 | |
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6 tremor | |
n.震动,颤动,战栗,兴奋,地震 | |
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7 chasm | |
n.深坑,断层,裂口,大分岐,利害冲突 | |
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