Since entering 2023, we have heard successively about earthquakes in our vicinity: successive strong earthquakes in Turkey and Syria, earthquakes in Tajikistan, earthquakes in Indonesia, earthquakes in Japan, and small earthquakes in Taiwan, Inner Mongolia, Qinghai, Hebei, Sichuan, Yunnan, Xinjiang, Gansu, Heilongjiang, Guangdong and other places in our country. Some friends ask why earthquakes occur? Do frequent earthquakes mean that there will be large earthquakes? What should we do?
(Ruins of Turkey's 2023 earthquake)
Where do earthquakes occur?
China is a country with frequent earthquakes, and earthquakes often occur in some areas, such as Sichuan, Yunnan and some places in northern Xinjiang will shake a few times every three forks and fives, so that the locals are not strange, what to do, they are too lazy to run. But there are places where you've never heard of an earthquake, why?
This is because earthquakes mostly occur in seismic zones, which in turn are often located in the fault zone of the earth. If a fault zone passes through a place, earthquakes are likely to occur in that place, and those far from the fault zone have little or no earthquakes.
(Frequent earthquakes on the Qinghai-Tibet Plateau and its surroundings)
The surface of our earth is covered with a thick crust, the thickest place of the crust is the Qinghai-Tibet Plateau, which is about 70 kilometers thick; The thinnest point is in the depths of the ocean, which is also 5 km thick. The earth's crust is made of hard rock, and it is very difficult to dig a hole in it.
However, the Earth's crust is only a thin, brittle shell relative to the Earth. If you shrink the earth to the size of an egg, the average crust is only one-fifth the thickness of an eggshell. Moreover, the earth's "eggshell" is broken, and it is full of large and small cracks, like a cracked tea egg.
(Crustal plates are like tea eggshells)
Scientists have found that volcanic eruptions, earthquakes and even strong earthquakes are more likely to occur at the intersection of the Earth's plates; Various geological fault zones created by plate extrusion deformation are also prone to earthquakes, while earthquakes occur less often far from these "cracks".
What are the root causes of earthquakes?
Most earthquakes are caused by crustal fault zones squeezing each other or by volcanic eruptions at plate fractures. The cracks of tea eggs do not squeeze each other, why does the shell of the earth move? This requires us to continue to dig down, deep into the earth to find the cause.
Like other rocky planets in the solar system, our earth has a huge iron core in the very center, the diameter of this iron core reaches 6900 kilometers, and its temperature is as high as 4000~6800 °C!
This huge iron ball constantly dissipates heat outward, making the mantle that wraps around it soft and creating convection in some hotter places, tumbling like we boil water. Of course, mantle convection doesn't roll that fast.
(The core heats the mantle to form thermal convection, which then pushes the crust to move)
The surface of the mantle is the earth's crust. The thermal insulation of the earth's crust is relatively good, even if there is magma with a high temperature of about 1000 ° C below, we will not feel hot feet. But we also said earlier: for the earth, the crust is very thin, it seems to float on the surface of the mantle, so when the mantle rolls, the crust will also be pushed to "slide".
The movement of the earth's crust is affected by the thermal convection of the mantle below, which causes the direction of the earth's crust to move inconsistently, pushing each other in many places, and many plateau mountains and ravines and deep valleys on the earth's surface are the result of plate squeezing and pulling.
The earth's crust is mainly a solid shell made of hard rock, which is not as easily deformed as plasticine. When the stress breaks through a certain critical point, the rock will suddenly break, the structural surface rubs against each other, and the huge energy is released instantaneously, and the release of energy is transmitted to a long distance through seismic waves.
(Earthquakes caused by crustal fault extrusion and stress release)
Now you know, human power can't stop earthquakes. The most fundamental reason is that the earth has a hot iron core, and only when the iron core cools down, the earthquake will disappear.
But certain human activities may trigger earthquakes, releasing stresses deep in the earth's crust early.
The known "reservoir earthquake" is one example: if people do not carefully carry out geological exploration before building the reservoir, or because the technical level is not enough to find a fault zone, the reservoir happens to be built near the fault, the reservoir water storage changes the surface pressure, or the water penetrates into the geological fault under strong pressure to reduce the friction coefficient, which will lead to the early release of stress accumulated in the rock, thereby inducing earthquakes. The frequent earthquakes at the source of the river in Guangdong are thought to be related to the construction of the Xinfeng River Reservoir, and most of its epicenters are located in the reservoir area, that is, near Wanlv Lake.
(An earthquake occurred in the Xinfengjiang reservoir area of Heyuan, Guangdong on February 11)
Whether human-induced earthquakes are good or bad, there are different theories in academia: some people believe that reservoir earthquakes are bad and may cause damage to the ground. Another view is that artificially induced earthquakes can release formation stress in advance and prevent it from accumulating too much, so that large earthquakes can be avoided.
Are there more earthquakes in 2023 than before?
Let's start by looking at how the number of earthquakes occurred globally in the first two months of 2023 compared to the same period in 2022:
Two-year earthquake comparison (source: "volcanodiscovery.com")
From the comparative data, it can be seen that the total number of earthquakes in the same time period is not much different, and there is a little less strong earthquake above magnitude 5. The difference is that the 2023 earthquake occurred in densely populated areas, causing a large number of casualties and property damage, thus attracting more attention.
According to data published by the International Earthquake Center (ISC) and the National Earthquake Information Center (NEIC), the number of earthquakes that occur globally each year does not change much. The number of times we can detect it with the instrument is about 500,000, of which about 100,000 are induced earthquakes.
"Increase" in the number of earthquakes above magnitude 5 (Source: International Earthquake Center)
One reason why some friends feel that there are more and more serious earthquakes than before is that with the development of economy and technology, scientists have deployed more and more sophisticated observation equipment around the world, and our technical means are more advanced, and small and medium-sized earthquakes in remote areas and deep oceans that were often ignored before can be detected and recorded. This is the reason for the increase in the black histogram and red dot plot in the image above.
Another factor is that the spread of information technology, especially the Internet, has broadened our horizons to events that were previously not covered by mainstream media. For example, in 1986, a magnitude 4 earthquake occurred in a city, and perhaps only local radio and newspapers carried out the broadcast; The 4.3 magnitude earthquake that occurred in Heyuan, Guangdong on February 11 quickly rushed to the hot search list, and the people of the whole country knew it.
Distribution of earthquakes in Asia in February 2023
Finally, let's summarize:
1. Earthquakes are caused by sudden sliding of faults in the earth's crust, which is random and inevitable. The thermal energy of the Earth's core pushes thermal convection of the mantle, which in turn causes the crust to rupture and plate movement and extrusion, and earthquakes occur when strong stresses are released instantaneously. Earthquakes often occur in one place, indicating that it is greatly affected by the movement of the earth's plates.
People who live near geological fault zones feel earthquakes more often, but from a global perspective, about 100,000 sensed earthquakes occur each year, and this number will not change much overall. Over the past 100 years, there have been about 16 major earthquakes of magnitude 7 or higher on the earth every year, of which 1989 was the fewest (6) and the highest in 2010, with a total of 23 earthquakes of magnitude 7 or higher.
3. Will earthquakes be more frequent in 2023? The answer will not be known until the end of the year. From the history of planetary evolution, earthquakes are the active manifestation of the earth's core, and when the temperature of the earth's core drops, the earth's magnetic field will disappear, and all living things will face extinction.
#地震 #