An earthquake is a shaking of the ground caused by the sudden breaking and shifting of large sections of Earth s rocky outer shell. Earthquakes are among the most powerful events on earth, and their results can be terrifying. A severe earthquake may release energy 10,000 times as great as that of the first atomic bomb. Rock movements during an earthquake can make rivers change their course. Earthquakes can trigger landslides that cause great damage and loss of life. Large earthquakes beneath the ocean can create a series of huge, destructive waves called tsunamis that flood coasts for many miles.
Earthquakes almost never kill people directly. Instead, many deaths and injuries in earthquakes result from falling objects and the collapse of buildings, bridges, and other structures. Fire resulting from broken gas or power lines is another major danger during a quake. Spills of hazardous chemicals are also a concern during an earthquake.
The force of an earthquake depends on how much rock breaks and how far it shifts. Powerful earthquakes can shake firm ground violently for great distances. During minor earthquakes, the vibration may be no greater than the vibration caused by a passing truck.
On average, a powerful earthquake occurs less than once every two years. At least 40 moderate earthquakes cause damage somewhere in the world each year. About 40,000 to 50,000 small earthquakes--large enough to be felt but not damaging--occur annually.
外研版英语六上MODULE 1《Unit 2 New York is in the east of America》word教案
外研版英语六下MODULE 3《Unit 1 The sun is shining》word教案
开心学英语六上《Unit 11 Let’s go to space》word教案(2)
开心学英语六上《Unit 3 How often do you go hiking》word教案(1)
外研版英语六上MODULE 2《Unit 2 Postcards from China》word表格式教案
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外研版英语六下MODULE 7《Unit 2 He spent about twenty-one hours in space》word学案
开心学英语六上《Unit 12 Review 3》word教案(1)
开心学英语六上《Unit 3 How often do you go hiking》word教案(2)
外研版英语六下MODULE 4《Unit 1 I`m making Daming`s birthday card》word学案2篇
开心学英语六上《Unit 11 Let’s go to space》word教案(3)
外研版英语六上MODULE 6《Unit 1 Apostcard from New York》word教案3篇
开心学英语六上《Unit 1 I wrote a long letter》word教案(2)
外研版英语六上MODULE 2《Unit 1 Chinatown in America》word教案2篇
外研版英语六下MODULE 5《Uint 2 He’s riding his bike, but it’s starting to rain》word学案
开心学英语六上《Unit 10 I want the best》word教案(2)
外研版英语六下MODULE 7《Unit 2 He spent about twenty-one hours in space》word教案2篇
外研版英语六下MODULE 9《Unit 1 What`s the matter》word教案2篇
开心学英语六上《Unit 7 He’s better than us》word教案(1)
开心学英语六上《Unit 5 It’s a magic hat》word教案(2)
外研版英语六下MODULE 9《Unit 2 Because it`s going to rain》word学案2篇
开心学英语六上《Unit 10 I want the best》word教案(1)
外研版英语六下MODULE 2《Unit 1 We`re going to have a picnic》word教案
外研版英语六上MODULE 7《Unit 2 Pandas love bamboo》word教案2篇
开心学英语六上《Unit 6 The turtle is faster》word教案(2)
外研版英语六上MODULE 5《Unit 1 Pleased to meet you》word教案
小学PEP新教材六年级下册英语教学计划
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开心学英语六上《Unit 4 Review 1》word教案
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