Have you ever seen a supermoon that can cause an earthquake?

The supermoon appeared in the night sky on the evening of June 14, and the Seven Planets in a Row astronomical phenomenon also appeared last night. Because the planets orbit the sun at different times, their arrangement and combination in the sky present various forms, and the Seven Planets in a Row is one of the rare ones. Saturn, Neptune, Jupiter, Mars, Uranus, Venus and Mercury will form this special astronomical phenomenon together.

But first, let’s learn some interesting facts about the moon!

Photographer: Ma Liang

In July 1969, after the astronauts on the Apollo 11 spacecraft landed on the moon, they set up an instrument to monitor moonquakes in the southwest corner of the Sea of ​​Tranquility on the moon. Since then, seismometers have been placed in different locations. The six seismometers on the moon have formed a network for monitoring moonquakes. From 1969 to 1977, the seismometers on the moon detected more than 10,000 moonquakes.

The difference between moonquakes and earthquakes:

1. Moonquakes last longer than earthquakes

On Earth, a small earthquake can cause a distant seismograph to vibrate for a minute, while on the moon it can last for an hour. Scientists believe this may be related to the lack of water on the moon and the fractured nature of the rocks.

2. Moonquakes occur less frequently than earthquakes

There are about 1,000 moonquakes each year, and about 5.5 million earthquakes on Earth each year.

3. The energy released by moonquakes is also much smaller than that of earthquakes

The largest moonquake is only equivalent to a magnitude 1-2 earthquake. According to statistics from the China Earthquake Networks Center, there were 81 earthquakes of magnitude 6 or above in the world in 2017. The largest earthquake was a magnitude 8.2 earthquake that occurred off the coast of Mexico on September 8, 2017. Based on the calculation that the energy of an earthquake differs by 33 times for every 1 magnitude difference in magnitude, the magnitude 8.2 earthquake that occurred off the coast of Mexico on September 8, 2017 was 1 billion times the energy of the largest moonquake on the moon.

4. Moonquakes have deeper epicenters

It is usually 700 to 1000 km below the lunar surface, while the focal depth of an earthquake is only tens of kilometers to 300 km.

5. Moonquake waves take longer to travel inside the moon

Moonquake waves are reflected and returned many times inside the moon, and last for nearly an hour, while the seismic waves of such small earthquakes on Earth last no more than a minute inside the earth. This is mainly related to the relatively dry and rough soil on the moon's surface, so moonquakes last longer. In addition, the moon's soil is very uneven, and the craters and cracks in the rocks on the moon's surface will scatter shock waves in all directions.

Through the data of lunar seismometer detection, scientists have discovered that the moon, like the earth, also has a layered structure inside. From the center to the lunar surface, the moon can be divided into the lunar core, lunar mantle and lunar crust. The specific thickness division of these three layers is based on the change in the speed of the moonquake waves. For example, at a depth of 65 kilometers from the lunar surface, the speed of the moonquake waves suddenly changes from 7 kilometers per second to 8 kilometers per second. The discontinuity of the wave speed indicates that the propagation medium inside the moon has changed. Based on this data, scientists infer that this should be the interface between the lunar crust and the lunar mantle. That is, the average thickness of the lunar crust is about 65 kilometers, of which the uppermost 1 to 2 kilometers are rock fragments and lunar soil.