53 Earthquakes-Mid

Earthquakes FOCUS Question How do earthquakes change Earth's surface?

地震如何改变地球表面?

Shaking Things Up It was the third game of the 1989 World Series. More than sixty thousand baseball fans packed Candlestick Park in San Francisco, California. But the fans got more action than they bargained for when the entire stadium shook for fifteen seconds. It was an earthquake! The game was called off. Luckily, the fans were unharmed. People in other parts of the city were not so fortunate. Although you may not feel the ground shaking, an earthquake is probably happening someplace on Earth right now. An earthquake is the shaking that occurs when enormous rocks in Earth's crust suddenly move and energy is released.

这是1989年世界大赛的第三场比赛。 加州旧金山的烛台公园挤满了6万多名棒球迷。 但当整个体育场震动15秒时，球迷们得到了比他们预期的更多的行动。 是地震!比赛被取消了。 幸运的是，粉丝们没有受伤。 城市其他地区的人们就没有这么幸运了。 虽然你可能感觉不到地面在晃动，但地震可能正在地球上的某个地方发生。 地震是地壳中巨大的岩石突然移动并释放能量时发生的震动。

Fault Formation Earth's crust—its outermost layer—is made up of many distinct pieces called tectonic (tek-TAH-nik) plates. These plates sit on top of a layer called the mantle, which is not as rigid and can flow. Currents in the mantle cause the plates to move slowly and continuously. This movement of Earth's plates is known as plate tectonics. Tectonic plates meet at plate boundaries, where they can separate, collide, or slide past one another. At plate boundaries, huge slabs of rock push and pull, and pressure builds up within them. If enough pressure builds up in the rocks, they break and form a fault— a crack in Earth's crust Most faults occur along plate boundaries, but they can also form in the middle of plates. Where there are faults, there are often earthquakes.

地壳——它的最外层——由许多不同的板块组成，这些板块被称为构造板块(tek-TAH-nik)。 这些板块位于地幔层的顶部，地幔不那么坚硬，可以流动。 地幔中的电流导致板块缓慢而连续地移动。 地球板块的这种运动被称为板块构造。 构造板块在板块边界相遇，在那里它们可以分离、碰撞或互相滑过。 在板块边界，巨大的岩石板块相互推拉，压力在其中积聚。 如果岩石中积累了足够的压力，它们就会断裂并形成断层——地壳中的裂缝。大多数断层沿板块边界发生，但它们也可以在板块中间形成。 哪里有断层，哪里就经常发生地震。

Earthquake Alert An earthquake begins when the land along a fault suddenly moves. The focus of the earthquake is the underground location where the land first moves. Waves of energy, called seismic (SIZE-mik) waves, radiate outward from the focus like ripples of water on a lake. This release of energy causes the ground to shake. The epicenter of the quake is the point on Earth's surface directly above the focus. It's where the strongest shaking occurs. During an earthquake, rocks on either side of a fault move in opposite direction—supward, downward, or sideways. This motion can abruptly change Earth's surface. Do You Know? Earthquakes can change Earth's rotation. A massive earthquake near Indonesia in 2004 made Earth spin a bit faster and slightly shortened the length of one day.

地震警报当断层上的陆地突然移动时，地震就开始了。 地震的焦点是地面首先移动的地下位置。 能量波被称为地震波(SIZE-mik)，从焦点向外辐射，就像湖面上的涟漪一样。 这种能量的释放导致地面震动。 地震的震中是地球表面上位于震源正上方的点。 这里是震动最强烈的地方。 地震时，断层两侧的岩石向相反的方向移动——向上、向下或向侧面。 这种运动可以突然改变地球表面。 你知道吗?地震可以改变地球的自转。 2004年印度尼西亚附近发生的大地震使地球自转速度加快，一天的长度也略有缩短。

Changing Earth's Surface Earthquakes change the surface and put people and structures at risk. During an earthquake, the displacement of rock can be small, moving Earth's surface less than a meter. But rock can also move several kilometers. A cliff, called a scarp, can form when an earthquake causes one side of a fault to push upward. Landforms such as valleys and ridges become offset (not lined up) where one side slides past the other. Normally, soil acts like a solid and can support the heavy weight of landforms and structures. But shaking makes some soil behave like a liquid. This process is called liquefaction. Liquefied soil can trigger landslides and mudslides. Bridges, buildings, and roads built on the loosened soil can collapse.

改变地球表面地震改变地球表面，使人们和建筑物处于危险之中。 在地震中，岩石的位移可能很小，使地球表面移动不到一米。 但是岩石也可以移动几公里。 当地震导致断层的一侧向上推动时，就会形成悬崖，称为断崖。 山谷和山脊等地貌在一侧滑过另一侧时发生偏移(不对齐)。 通常情况下，土壤就像固体一样，可以支撑沉重的地形和结构。 但是震动会使一些土壤表现得像液体。 这个过程被称为液化。 液化的土壤会引发滑坡和泥石流。 建造在松软土壤上的桥梁、建筑物和道路可能会倒塌。

Measuring Up More than a million earthquakes happen around the world each year. Most are so minor that you wouldn't even feel them, while others are massive. One way to measure and compare the strength, or magnitude, of earthquakes is to use the Richter scale. On this scale, larger numbers indicate more powerful earthquakes. Each higher number on the scale represents an increase of about thirty-one times more energy. Scientists also use the moment magnitude scale (below). This scale is based on the total energy recorded for an earthquake. As with the Richter scale the higher the number, the larger the earthquake and the more energy it has.

全世界每年发生100多万次地震。 大多数是非常小的，你甚至感觉不到它们，而其他的是巨大的。 测量和比较地震强度或震级的一种方法是使用里氏震级。 在这个范围内，数字越大，地震强度越大。 体重秤上的数字每高一个，就代表能量增加了大约31倍。 科学家们也使用矩量级(如下图)。 这个等级是根据地震记录的总能量计算的。 与里氏震级一样，数字越高，地震强度越大，能量也就越大。