What causes earthquakes? The outer layer of the Earth is divided into huge pieces that are constantly moving. When two of the pieces move against each other or move in opposite directions, an earthquake happens. A large movement causes a violent earthquake, and a small movement causes a mild one. There are thousands of earthquakes every year, but most of them are very small.

The place where an earthquake begins is called the epicenter. When an earthquake happens, vibrations move outward from the epicenter. These rolling vibrations are called seismic waves. Usually, an earthquake is only strong enough to cause damage near its epicenter.

When the epicenter of an earthquake is at the bottom of the ocean, it can create huge sea waves as tall as fifteen meters. These waves cross the ocean in several hours. Rushing toward land, they destroy small islands and ships in their path. When they hit land, they flood coastal areas far from the epicenter of the earthquake. When a huge tsunami happened in the Indian Ocean in 2004,the wave reach two kilometer inland, killing 230000 people in eleven countries

After an earthquake happens, people can die from lack of food, water, and medical supplies. The amount of destruction caused by an earthquake depends on where it happens, what time it happens, and how strong it is. It also depends on the types of buildings in the area, the soil conditions, and the size of the population. Of the thousands of earthquakes in the world each year, only about one in 500 causes damage.

In 1556,an earthquake in northern China killed 830,000 people－the most in history. At that time, there was no way to measure its strength. In 1935, scientists started using the Richter Scale to measure seismic waves. A seriously destructive earthquake measures 6.5 or higher on the Richter scale (this has now been largely replaced by the Moment Magnitude scale which uses the same scale system, but is more accurate).

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• Lv 4
7 年前
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什麼原因導致地震？外層的地球被劃分成不斷移動的大塊。當兩個片斷的互相反對移動或向相反方向移動時，就會發生地震。一個大型的運動導致一次猛烈的地震，和一個小運動導致一種溫和。每年都有數以千計的地震，但大部分都是非常小。地震的開始位置的地方稱為震央。當地震發生時，振動從震央往外移動。這些滾動的振動稱為地震波。通常，在震央附近的災情最為慘重。有一次地震的震央在海底時，它可以創建高度達十五米的巨大海浪。在幾個小時內海嘯沖衝陸地，摧毀島嶼和船舶。在2004年在印度洋發生巨大的海嘯，海嘯沖擊陸地二公里之內，在 11 個國家的 230000 人喪生。地震發生後，人們缺乏食物、 水和醫療用品。地震造成的毀滅性發生的地點、 什麼時候它會發生，和它是多麼強大。它還取決於建築領域、 土壤條件和人口規模的類型。在世界各地每年都發生數以千計的地震，只有約 500件造成嚴重損壞。在 1556 年，歷史上北中國的地震死了 830,000人民 。那時候，沒有辦法來衡量地震強度。1935 年，科學家們開始利用裡氏衡量地震波。嚴重破壞性地震的措施 6.5 或更高裡氏 （在現代已被取代，使用更具規模的系統，且更準確地震測試) 。

參考資料： 自已
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