Here can be a simple answer, the earthquake is not a "specialty" of the earth. There are also earthquakes on the moon. Because it happened on the moon, we call it a "moon earthquake". However, the moon earthquake and earthquake are very different! Explore the mystery of the lunar earthquake; Starting from "Apollo 1 1", six lunar seismographs have been set up in different parts of the moon. This instrument is very sensitive. Even the tiny vibration of one millionth of the smallest earthquake that humans can feel can be recorded truthfully and transmitted back to the earth through the communication system.
As soon as the seismograph appeared on the moon, it immediately showed its talents. 1On the wing day of July, 969, the day after Apollo 1 1 landed on the moon, the seismograph won its first battle and was sent back to Earth accurately. The cause of this lunar earthquake is unknown, but it is wonderful compared with the earthquake! In September of the same year, Le issam, the designer of lunar seismograph and the lamont de Hajo Institute of Geology of Columbia University, gave a special lecture on lunar earthquakes at a seminar co-sponsored by the National Geodetic Association and the International Geophysical Association in Madrid, Spain. He said: "There are no P waves and S waves in the monthly earthquake records; Surface waves cannot be clearly distinguished. " All the scientists sitting here are surprised by his report. As we all know, when an earthquake occurs, people first feel longitudinal waves, then shear waves and finally surface waves. There is no such difference between lunar earthquakes, which is of course incomprehensible. How do you explain this? In June+10 of the same year, issam himself explained: "At present, the lunar seismograph records almost all the vibration of the instruments inside the lunar module, not the lunar earthquake." By the way, all the vibrations of astronauts on the moon are recorded by the lunar seismograph and sent back to Earth, because the lunar seismograph of Apollo 1 1 is only 17 meters away from the lunar module. Apollo 12 lunar seismograph was set 30 meters away from the lunar module. It also recorded a wonderful vibration, which was small at first, then the amplitude increased slowly, and finally it decayed very slowly at an unimaginable speed. On average, such vibrations can be recorded four times a day. The duration of the whole vibration varies from a few minutes to 1 hour, which is uneven and very different from the earthquake scene on the earth. The vibration of the earth is usually a few tenths of a second, and the longest is only a minute or two. The most incredible thing is that, as issam pointed out, these vibrations on the moon can't clearly distinguish longitudinal waves, shear waves and surface waves. In order to distinguish it from the real lunar earthquake to be discussed below, we call this inexplicable vibration described above L-shaped.
Interestingly, L-shaped vibration can also be obtained through "artificial lunar earthquake". As mentioned earlier, the lunar module consists of ascending section and descending section. After the lunar activity, the ascending segment will return to the mother ship with the astronauts on the moon. Once the mission is completed, the ascending segment will be thrown back to the moon, resulting in the so-called "artificial lunar earthquake".
The Apollo 12 artificial lunar earthquake occurred 76 kilometers away from the lunar seismograph. The records of lunar seismograph show that the vibration lasted for more than an hour from occurrence to increase until disappearance, which is no different from L-shaped vibration.
Based on this, it can be considered that L-shaped vibration is not caused by the interior of the moon. After further experiments and analysis, it is concluded that most L-shaped vibrations are caused by the landing of tiny meteorites from space. 1972 In May, a meteorite with a diameter of 3 meters fell near the lunar seismograph "Apollo 1 1", which triggered an obvious lunar earthquake.
Does this mean that the moon will not vibrate from the inside? The lunar seismograph clearly tells us that it won't. However, even this kind of vibration-a real lunar earthquake-has completely different characteristics from earthquakes on earth.
First of all, a major feature of the lunar earthquake is; Small scale, low frequency and deep source. During the observation period of about three years, the largest monthly earthquake was only about 2.5. This kind of earthquake happens on the earth, which can be said to be a common occurrence, but it is rare on the moon. Apollo 14 and Apollo 16 recorded 170 true moon earthquakes in one month, while Apollo 12 and Apollo 15 only recorded 60 times.
In these vibrations, nine sources can be determined. Surprisingly, the focal depths of lunar earthquakes are all between 600 and 1000 km. The shaking part occurs in the crust of tens of kilometers, and earthquakes with a depth exceeding 100 kilometers are rare, and the deepest source is within 700 kilometers. In other words, earthquakes occur on the surface of the earth, while lunar earthquakes often occur in the "internal organs" of the moon.
Secondly, after detailed research, it is found that there are at least 40 places on the moon where lunar earthquakes-lunar earthquake nests occur repeatedly. Moreover, even this veritable lunar earthquake cannot clearly distinguish longitudinal waves, shear waves and surface waves. At the same time, the vibration time is surprisingly long, and it is not surprising that it lasts for more than an hour.
Why do lunar earthquakes have these unique characteristics? Some scientists believe that this is because on the surface of the moon, the shock wave of the moon is scattered seriously. Scientific experiments have confirmed this conclusion. When the scattering is strong, P wave, S wave and surface wave are really confused and difficult to distinguish.
However, readers with earthquake knowledge may ask, if the scattering is large, the attenuation will be serious, so the propagation distance should not be too far. On the other hand, the moon earthquake can spread to a distance of more than 1000 km. How to explain it?
Based on the experiments on lunar rocks, scientists have made this explanation, saying that this is because the absorption rate of lunar rocks to vibration waves is very low in a high vacuum environment. As we all know, the moon is almost completely vacuum, so it is also highly vacuum in the cracks in the rocks that make up the surface of the moon. In this environment, the moon shock wave can travel far. "
To sum up, the moon is not a peaceful "paradise". Like our earth, there will be vibrations from time to time, which means that vibration is by no means a "specialty" of our earth. But what is the cause of the earthquake? To understand this question is probably the same as answering the cause of the earthquake, which requires us to continue to explore and study!