How big is the largest earthquake in human history? What is the limit of earthquakes?

The China Earthquake Networks Center officially determined that a magnitude 7.9 earthquake occurred in Myanmar (21.85 degrees north latitude, 95.95 degrees east longitude) at 14:20 on March 28, with a focal depth of 30 kilometers. In addition, the earthquake was felt across Thailand, and the tremor lasted for several minutes in Bangkok, and people left high-rise buildings and poured into the streets.

The epicenter of the 7.9-magnitude earthquake in Myanmar is 294 kilometers away from the nearest border of my country, causing strong earthquake feelings in Xishuangbanna, Dehong, Kunming, Lijiang, Baoshan, Dali and other places in Yunnan. Earthquake feedback was also felt in Guizhou and Guangxi and other places.

The world's largest earthquake so far this year

According to CCTV News, this earthquake is the 17th earthquake of magnitude 6 or above in the world this year, and it is also the largest earthquake so far this year.

Based on the preliminary earthquake parameters, the Tsunami Warning Center of the Ministry of Natural Resources judged that the earthquake may trigger a local tsunami around the epicenter, but because the epicenter is outside the Pacific Ocean, it will not affect China's coast.

The largest earthquake ever recorded

When it comes to earthquakes, everyone has fear in their hearts. Can you imagine what a 9.5 magnitude earthquake would be like?

At 3 p.m. on May 21, 1960, a magnitude 9.5 earthquake struck Chile. From that day to May 30, the country was hit by several earthquakes in succession, during which six dormant volcanoes erupted again and three new volcanoes appeared.

This was a swarm earthquake. Over a period of more than a month, hundreds of earthquakes occurred in a narrow strip of land 1,400 kilometers long from north to south. Among them, three were above magnitude 8 and ten were above magnitude 7, which is rare in the world's earthquake history.

At the same time, the earthquake also caused the largest tsunami in the 20th century. Most of the buildings along the coast of Chile were swept away by the waves. This was the largest earthquake in the world since instrumental records, with the strongest magnitude of 9.5 and the fault 25 kilometers below the surface.

The Chilean coast after being hit by the tsunami Source: wikipedia.org

Chile is located in the Pacific Ring of Fire, an area of ​​high seismic activity caused by the collision of the Nazca Plate, the South American Plate, and the Chiloé Plate, with the Nazca Plate subducting between the latter two.

Image source: wikipedia.org

These geological features have led to Chile being ranked as the most seismically active country in the world. To date, more than 100 magnitude 7 earthquakes and 12 major tsunamis have been recorded.

What is the highest magnitude earthquake that can occur on Earth?

An earthquake of magnitude 10 has never been encountered in human history, but is it possible for us to encounter an earthquake of magnitude 10 or above?

The magnitude of an earthquake is generally measured using the Richter magnitude, which is calculated using the common logarithm of the maximum amplitude of the seismic wave recorded by the seismograph at the observation point. The calculation formula for the Richter magnitude is as follows:

log10E = 4.8 + 1.5M

E represents the energy released by the earthquake, and M represents the magnitude of the earthquake. From this formula, we can calculate that for every 1 difference in magnitude, the energy released will differ by about 32 (101.5) times, and for a 2-magnitude difference, the energy difference will reach 1,000 times.

According to the calculation formula of the Richter magnitude, we can calculate that the energy released by a magnitude 1 earthquake is

E = 104.8+1.5×1 ≈2×106 joules

With the above formula, we can calculate that the energy released by a magnitude 10 earthquake is about 6.3×10^19 joules. The energy released by the "Little Boy" atomic bomb dropped by the United States on Hiroshima, Japan in 1945 was about 5.3×10^13 joules. According to the above calculation, a magnitude 10 earthquake is roughly equivalent to the energy released by 1 million "Little Boy" atomic bombs . If this energy is dispersed around the world, it is enough to destroy human civilization dozens of times.

In fact, an earthquake of magnitude 9 or above is enough to make the Earth "tremble" and slightly change the Earth's rotation time. For example, the two magnitude 9 earthquakes in history changed the Earth's rotation by about one millionth of a second. If a magnitude 10 earthquake really occurs, it will not only change the Earth's rotation time, but the entire human society is expected to be greatly affected.

From the perspective of geological conditions, a magnitude 10 earthquake is still possible. A magnitude 10 earthquake is a very large earthquake and can only be caused by a fracture in the crust. Take the 1960 Chile earthquake as an example. The earthquake was magnitude 9.5 and was caused by a fracture in the crust of about 1,000 kilometers long. Assuming that the energy released by the rock is proportional to the length, then according to this estimate, to trigger a magnitude 10 earthquake, it is estimated that a fracture in the rock layer of about 5,000-6,000 kilometers is required. Such a large fracture in the rock layer requires a fault line of comparable length. The longest fault line in the world is in the Sanda large thrust area, located on the western coast of Southeast Asia, with a length of about 5,500 kilometers. If the entire fault line breaks at the same time, it is possible to trigger a magnitude 10 earthquake.

Schematic diagram of the Songda large-scale thrust area - red line in the figure

If we consider the structure of the earth itself, a magnitude 10 earthquake is possible, but the probability is very small, and this will also be the upper limit of earthquakes on earth . If an earthquake of a larger magnitude occurs, it is estimated that it can only be caused by a devastating meteorite impact or a large-scale nuclear war. In either case, the entire human civilization will not be able to escape.

Source: @China Earthquake Networks Express, Beijing Youth Daily, "Institute of Physics, Chinese Academy of Sciences" WeChat account, China Geography