“Earthquake clouds”, “red light in the sky”… Were there early signs of the Shandong earthquake?

According to the China Earthquake Networks Center, at 2:33 a.m. on August 6, a magnitude 5.5 earthquake occurred in Pingyuan County, Dezhou City, Shandong Province, with a focal depth of 10 kilometers.

The picture is taken from the official website of China Earthquake Networks Center

Every earthquake is always accompanied by close attention and discussion, and this time is no exception. After the Shandong Plain earthquake, many "strange phenomena" related to earthquakes appeared on the Internet, such as "earthquake clouds", "red light in the sky", "animal migration", etc. So, how did the earthquake happen, and are these so-called "strange phenomena" related to the earthquake? Today we will take a closer look at these old rumors.

How are earthquakes formed?

If you want to thoroughly understand these rumors, you need to have a clearer understanding of the principles of earthquake generation.

Simply put, underground rock strata are pulled and deformed and accumulate energy under the action of tectonic movements. Once the limit that the strata can withstand is exceeded, fractures and dislocations will occur and energy will be released. This process of energy release is an earthquake.

For the sake of ease of understanding, if we simplify the stratum into a "chopstick", then the process of an earthquake can be understood as the process of the chopstick being "broken". Energy accumulates in the process of both hands gradually exerting force. The moment the chopstick is broken corresponds to the occurrence of an earthquake. The location where the chopstick is broken is what we usually call the epicenter.

Schematic diagram of a strike-slip earthquake. Photo courtesy: Zhang Guangli

However, the underground medium during an actual earthquake cannot be as simple as a "chopstick". At this time, the seismic waves generated with the epicenter as the center propagate in all directions, causing ground ruptures and vibrations within a certain range, posing a threat to our lives and property safety.

Rumor 1: Clouds can predict earthquakes

First of all, the earth is made up of different spheres. The lithosphere, asthenosphere and inner sphere together make up the solid earth. According to the principle of earthquakes, the essence of earthquakes is the tectonic movement underground, which has no direct connection with the clouds in the sky .

The entire process of cloud formation takes place in the atmosphere, while earthquakes occur in the underground lithosphere. The difference between the two is huge.

If you often look up at the sky, you will find that the so-called "earthquake clouds" on the Internet are actually just the more common altocumulus, stratocumulus or cirrocumulus clouds in life, which appear in wavy, fish-scale or radial shapes in the sky . The appearance of these clouds may indicate changes in the weather, but if clouds are regarded as precursors to earthquakes, there is absolutely no scientific basis . In this regard, officials from the China Meteorological Administration and the Earthquake Administration have repeatedly refuted the rumors that the so-called "earthquake clouds" have nothing to do with earthquakes.

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Rumor 2: The "red light in the sky" is related to the earthquake

In addition to the "earthquake clouds", there is also a saying circulating on the Internet that "red light appears in the sky" before an earthquake. In particular, "red light" appeared in the sky in many places before and after the Shandong Plain earthquake. Many people suspect that this "phenomenon" is related to the earthquake, which is also an unfounded statement .

In fact, we often see red light in the sky in our daily life. The reason for its appearance is the scattering of sunlight after entering the atmosphere, and it has nothing to do with the movement of underground media . There is no need to panic because of this "red light" in the sky.

Rumor 3: Earthquakes often occur in summer and at night

In addition to weather phenomena, there is also a saying that earthquakes usually occur in summer and more often at night. This is actually a cognitive illusion .

First of all, the occurrence of earthquakes has nothing to do with seasons . Seasonal changes are caused by the movement of celestial bodies between the earth and the sun, which will bring about temperature changes on the earth's surface. But the impact of seasonal changes on the internal matter of the earth is negligible .

In response to this problem, earthquake researchers have counted earthquake data from the global seismic network and found that the number of earthquakes above magnitude 6 in summer and winter around the world in the past decade is very small. Similarly, the sound during the day and night is even smaller, so the claim that earthquakes occur more frequently at night is also unfounded .

However, it should be noted that once an earthquake occurs at night, its harm will definitely be greater , because people who are asleep at this time may not be able to notice the earthquake warning information and make timely evacuation responses.

Rumor 4: Animals can predict earthquakes

Another theory about earthquakes is that various "abnormal behaviors" of animals can be used to predict earthquakes, such as dogs barking at home, toads migrating in groups, birds flying around, etc. Because animals have an auditory system that exceeds that of humans, they can sense the upcoming earthquake .

But there is actually no scientific basis for the idea that abnormal animal behavior can predict earthquakes .

You know, there are many reasons for animals' abnormal behavior, such as ambient temperature, air pressure, humidity; surrounding gas smell, sound; animal living habits, etc. Therefore, animals' abnormal behavior cannot be considered as foreknowledge of a major earthquake . Take the "flocks of toads" mentioned by many rumor-mongers, for example. In fact, it is toads gathering to lay eggs.

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In addition, there are actually many relevant statistical studies at home and abroad on the issue of "animals predicting earthquakes" . Researchers have indeed found that some animals show abnormal behavior before some major earthquakes, but there are also no abnormal animal behavior before some major earthquakes .

Therefore, it is impossible to determine whether abnormal animal behavior is related to earthquakes. The author believes that it is obviously unscientific to use the "abnormal activities" of certain animals to predict earthquakes. The "abnormal behavior" of animals is difficult to define, and there are too many influencing factors.

Although earthquakes are scary, don't believe rumors!

Why are there so many rumors related to earthquakes? In the final analysis, it is because the public currently does not understand the nature of earthquakes enough, and fears are generated by the unknown . People believe that earthquakes are rare and abnormal disasters, so they want to link earthquakes with certain "strange phenomena" in life, so there are sayings such as "earthquake clouds", "red light in the sky" and "animal abnormalities".

In fact, earthquakes are natural phenomena on Earth, just like typhoons, rainstorms, and volcanic eruptions. From ancient times to the present, the Earth we live on has never stopped "vibrating". There are about 5 million earthquakes on Earth every year, and tens of thousands of earthquakes every day . However, most of them are too small or too deep to be felt by people. Among them, there are about 10 to 20 earthquakes above magnitude 7 that can really cause serious harm to humans every year; there are only one or two earthquakes that can cause particularly serious disasters like Tangshan and Wenchuan every year. Therefore, there is no need to be afraid of or panic about earthquakes themselves .

Secondly, the so-called "strange phenomena" in life are usually due to our inadequate observation and understanding of natural phenomena. Once we understand the nature of these phenomena from a scientific perspective, we will no longer find them so mysterious and abnormal . Let the general public truly understand the nature of natural phenomena, which is also one of the important meanings of our current popular science work.

At present, earthquake prediction and forecasting is a scientific problem recognized by the world and is in the exploratory stage both at home and abroad . Earth scientists and seismologists around the world are working hard to explore the theory and methods of earthquake prediction and forecasting. At present, there has been no scientific breakthrough in earthquake prediction .

Author: Zhang Guangli, PhD in Seismology, Institute of Geology and Geophysics, Chinese Academy of Sciences

Review | Chen Huizhong, Researcher at the Institute of Earthquake Prediction, China Earthquake Administration

Shen Ping, Researcher at the Institute of Geophysics, China Earthquake Administration