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In this world, when the word natural disaster is mentioned, I am afraid that the first word that comes to many people's minds is "earthquake", followed by words such as typhoons, tsunamis, volcanic eruptions, mudslides, floods, etc., and some people even say words such as comets hitting the earth.

Yes, the so-called natural disasters refer to the abnormal phenomena that occur in the natural world on which human beings depend, and the harm caused by natural disasters to human society is often shocking.

According to the severity of the consequences caused by natural disasters, human beings have divided the possible natural disasters into nine levels, but the funny thing is that the top three are all celestial disasters, that is, the catastrophic consequences caused to the earth by factors other than the earth. For example, the number one is the death of the sun, which becomes a red giant and then devours the earth; In second place, the so-called black hole tearing and engulfing the earth is even more unobtrusive; As for the third place, it is a little more reliable, that is, the asteroid hit the earth.

Well, we have to admit that the above three natural disasters are the ultimate disasters for human beings or for the entire earth, but the probability of these three natural disasters is too small, or too long

And in the interior of the earth, earthquakes rank first in terms of the severity of the consequences of natural disasters. And earthquakes are also the fourth of the nine scales above.

Earthquake, also known as ground motion and ground vibration, is a natural phenomenon that causes vibration during the rapid release of energy from the earth's crust, during which seismic waves will be generated. Earthquakes often cause serious casualties, which can cause fires, floods, toxic gas leaks, the spread of bacteria and radioactive materials, and may also cause secondary disasters such as tsunamis, landslides, collapses, and ground fissures.

After counting the various natural disasters recorded by mankind, the casualties caused by earthquakes are undoubtedly the first to be ranked. We won't talk about the earthquakes in the distance. The recent earthquakes alone, with the serious consequences of the disasters of this life, are so bloody

Whether it is the Kanto earthquake that occurred in the twenties of the last century, or the Tang Dynasty in the seventies of China. The Great Earthquake and the New Century of Wen. The Sichuan earthquake, or the Indian Ocean tsunami caused by the Indian Ocean earthquake, caused hundreds of thousands of deaths

And the earthquake that struck in 2011. Although the resulting tsunami did not cause significant casualties, it directly caused the Fukushima nuclear power plant to leak, and the consequences were even more serious than the direct consequences of the earthquake

Earthquakes are a punishment for human beings!

However, with the current human technology, it is not possible to predict the occurrence of an earthquake before it occurs, and it can only provide early warning after the earthquake, providing people in the earthquake area with preparation time ranging from a few seconds to tens of seconds.

This technique is very simple to say, and it is to take advantage of the difference in the propagation speed of P waves (longitudinal waves) and S waves (transverse waves) in the event of an earthquake to provide early warning.

After an earthquake occurs at an underground source, the energy released travels in the form of two waves. One is the compression wave (referred to as P wave) generated by squeezing rock, and its vibration direction is consistent with the propagation direction of the wave, so it is also called longitudinal wave, which makes the ground jolt up and down; One is the shear wave (referred to as S wave) generated by shearing rock, and its vibration direction is perpendicular to the propagation direction of the wave, so it is also called a transverse wave, which makes the ground shake from side to side. The transverse wave is much stronger than the longitudinal wave, and the amplitude is 3~10 times that of the longitudinal wave. It is a major contributor to earthquake disasters. But transverse waves travel at a slower speed of about 4 kilometers per second. Whereas, longitudinal waves travel at a speed of about 7 kilometers per second.

So it's not hard to think about whether it is possible to take advantage of the time difference between these two wave speeds, and once a longitudinal wave is detected, it can give an early warning before the arrival of a highly destructive transverse wave. The warning time may only be a few seconds or a dozen seconds, although it is too late to evacuate the crowd, but there is time to take measures such as cutting off gas, stopping power generation, and stopping high-speed trains. Prevention of secondary disasters. If it is far enough away from the epicenter, the warning time may even be as long as tens of seconds. The distance between Yingxiu, the epicenter of the Wenchuan earthquake, and Beichuan, the worst-hit earthquake, is about 120 kilometers in a straight line, and if an early warning is issued to Beichuan immediately after Yingxiu detects the longitudinal waves, then Beichuan can have about 30 seconds to react, which is even enough to organize students to evacuate the school building.

The principle is simple, though. However, it is not easy to build a national earthquake early warning system based on this, and at least three conditions must be met.

First of all, it is necessary to have a dense network of seismic stations to monitor the situation in all parts of the country in a timely manner.

Second, this is an expensive and huge project, and if we want to develop this project, we must have the financial resources, ability and willingness to develop it.

The last condition is better described as a contradiction than a condition. Because when an earthquake occurs, the epicenter area with the most damage does not have time to give warning, and the farther away from the epicenter, the longer the warning time, but the smaller the earthquake damage, the less early warning is needed. So, this becomes a key factor that makes people conflicted. Do? Or don't do it? Spending a lot of money to get this system out, is it really that useful?

In fact, perhaps it is because of the last reason that only one country in the world has established an extremely complete earthquake early warning system, and that is the original earthquake.

To say that it is really a poor country, it is an island country in itself, but it is located in Northeast Asia, where earthquakes occur most frequently in the world.

It occupies only 0.28% of the world's land area, but 10% of the world's earthquakes and 7% to 10% of volcanic activity occur in the world. This year's earthquakes released 10% of the world's energy.

Are you unlucky, you say?

It is precisely for this reason that the national earthquake early warning system began to be tested in February 2004, and by June 2006, a total of 855 warnings had been issued, of which only 26 were false alarms, and the effect seemed to be good, so it was officially put into use in October 2007.

This expensive system consists of Hi-net, a high-sensitivity seismic network consisting of 864 stations, a strong seismic network K-net consisting of 1,028 stations, a baseplate strong seismic network consisting of 688 stations, a broadband seismic network consisting of 83 broadband seismic stations, F-net, and a Japan Meteorological Agency (JMA) seismic network consisting of 205 stations.

The system is connected to a TV/mobile phone system and has the right to send notifications directly. The number of mobile phones is as high as 240 million, and there are nearly two mobile phones per person, so once this system issues an early warning, almost all of them can make preparations at the first time.

This is the reason why only one country in the world can truly achieve "ten-second earthquake warning"! It is also the main reason why the population density is so large, and there are frequent earthquakes of magnitude 7 or higher, but the number of deaths is so small.

And today, this earthquake early warning system, which covers the entire mainland and overseas territories, has issued an early warning message that can be seen by everyone at almost the same time

[It's about to be 515, I hope to continue to hit the 515 red envelope list, and the red envelope rain will be able to give back to readers and promotional works on May 15. A piece is also love, and it must be better! (To be continued.) )