CNN News:地震夷平意大利小镇 解读地震预警系统

The mayor of Amatrice, which is located in central Italy, says his town is no more. When a powerful 6.2 magnitude earthquake struck early Wednesday, Amatrice was at the epicenter. That's the point in the earth's surface directly above where the earthquake occurred. The town's clock tower, its time stopped at the moment the earthquake hit, was one of the only structures still standing. Rescue efforts have been going on around the clock.
Volunteers have been using their bare hands to dig through rubble. There are several Italian villages that were affected. They're in remote mountainous areas that can be hard to reach.
Italy's prime minister says the quake killed at least 120 people, but warned that toll could increase. The quake was felt as far away as Rome, 100 miles from the epicenter. And dozens of aftershocks have been reported. Pope Francis asked people to pray for those affected.
Earthquakes are entirely uNPRedictable. There are warning systems that can save some lives, but only under certain conditions.
意大利中部城镇阿马特里切的市长表示，他所管辖的城镇已经不复存在。周三清晨，6.2级强地震重创意大利，阿马特里切就位于震中附近。震中指震源在地球表面上的垂直投影点。阿马特里切镇的钟楼时针停止在地震发生的时间，这座钟楼是目前仍屹立不倒的建筑之一。救援工作仍在日夜不间断地进行。
志愿者一直徒手在废墟中挖掘。意大利有数座村庄受灾。这些村庄位于难以到达的偏远山区。
意大利总理表示，这起地震至少造成120人死亡，他警告称，死亡人数可能还会上升。地震发生时，距震中100公里远的罗马都有震感。目前震区已发生数十起余震。教皇弗朗西斯希望人们为灾民祈祷。
地震完全无法预测。地震预警系统可以挽救一些生命，但前提是要满足特定的条件。

CHAD MYERS, cnn CORRESPONDENT: If you're in an epicenter of an earthquake, you're going to get no warning. There's no time for that.
The warning depends on the distance you are to the earthquake epicenter.
SUBTITLE: Earthquake early warning system.
MYERS: An early warning system for earthquakes is expensive and also complex. Part of the problem is we don't have a system that can predict the earth is going to move. Our warming system is based on the fact that the earth is already moving and then if you're farther away from that epicenter, we can give you some time to prepare. Some minor time but some time.
Unlike a tornado warning where Doppler Radar can see the rotation and issue a warning before the tornado, an earthquake warning happens when the earthquake is already shaking. Another limitation is how close the sensor is to the epicenter. If the sensor is 10 miles away from the epicenter, it takes five seconds to get to that sensor. So, the more sensors we get, the better the lead time we'll get as well.
If we get 10 seconds notice of an earthquake that's happening, especially a big one, you can open up the elevators on the nearest floor. You can stop trains. You can stop all those things that are moving before the shaking gets there.
This entire system works because of the speed of light, or the speed of the warning going down the line, is 186,000 miles per second. The earth as it's wiggling and shaking along is going at 2 miles per second.
So, if you're 30 miles away, your warning could be 15 seconds. It's 15 seconds that could save your life.
cnn记者查德·迈尔斯：如果你在震中区，那你不会收到地震预警。因为没有时间进行预警。
地震预警取决于你距离震中区的距离。
副标题：地震预警系统
迈尔斯：地震预警系统造价高昂又复杂。部分问题在于我们没有可以预测地球移动的系统。我们的预警系统是在地球已经发生移动后，对距离震中较远的地方发出预警，给当地留有一定的应对时间。虽然时间很短，但至少有准备时间。
多普勒雷达可以探测旋转变化并在龙卷风发生前发布预警，可是与龙卷风预警系统不同，地震预警是在地震发生后发出的。另一个限制是传感器距离震中的远近。如果传感器距离震中10公里，那传感器感到地震需要5秒钟的时间。所以，传感器的数量越多，我们得到的预警时间越有利。
如果我们在地震发生10秒钟前接到预警，尤其是在大地震中，那我们就可以打开最近楼层的电梯。可以让火车停驶。可以在被地震波及前停止所有正在运行的设施。
整个地震预警系统依靠光速或者说是预警信息传递速度运行，该速度达到每秒18.6万英里。而地震波的传播速度为每秒2英里。
也就是说，如果你距离震中30英里，你可能有15秒钟的预警时间。这15秒钟时间，就可能挽救你的生命。