At 2:33 on August 6, 2023, a 5.5 magnitude earthquake struck Pingyuan County, Dezhou City, Shandong Province. When the earthquake occurred, the epicenter and surrounding residents were woken up, and many citizens in Beijing, Tianjin, Liaoning, Hebei, Henan, Anhui, Jiangsu and other neighboring provinces and cities received early warning that seismic waves were about to arrive.
As one of the major natural disasters, the disasters caused by the earthquake have left unforgettable memories, such as the 1976 Tangshan earthquake and the 2008 Wenchuan earthquake in mainland China.
So, what are the patterns of earthquakes? Can it be predicted?
Unfortunately, little is known about earthquakes, but knowledge of earthquake-related science can minimize damage.
2008 Wenchuan earthquake site (picture from Tuworm.com)
Plate movement
It is still a mystery when earthquakes began to occur on Earth, but the earliest record of earthquakes in human history is found in the earthquake event of the Yellow Emperor in the Bamboo Book Chronicle, which is more than 4,000 years old. The ancients' descriptions of earthquake phenomena and their causes are mostly mythical.
With the development of science and technology, human beings use scientific instruments to observe earthquakes, record seismic data and analyze them, and then gradually rationalize and objective understanding earthquakes.
An earthquake is a phenomenon in which the ground vibrates within a certain range caused by a shock wave caused by a sharp rupture in the earth's interior. The pressure and collision between plates on the earth causes displacement and rupture on the edge of the plate and inside the plate, which is the main cause of earthquakes.
Earth vibration is the most intuitive and common manifestation of earthquakes. A strong earthquake that occurs on the seabed or in a coastal area can cause large waves, called tsunamis. Severe earthquakes in land areas can cause secondary disasters such as landslides, collapses, and ground fissures.
Tsunamis are manifestations of seabed earthquakes (Figure: Fig worm)
Earthquakes with the same magnitude have different degrees of damage to the ground due to different focal depths. The shallower the epicenter, the greater the damage, but the smaller the scope of the impact. Therefore, highly destructive earthquakes are generally shallow source earthquakes, such as the 1976 Tangshan earthquake, which had a focal depth of only 12 kilometers.
In order to intuitively express the size of the earthquake, scientists formulate a measurement according to the amount of energy released by the earthquake, which is expressed by "level". Earthquakes less than magnitude 3 are weak earthquakes and are generally not easy to detect; Earthquakes greater than 4.5 and less than 6 are medium-strong earthquakes and will cause certain damage, but the severity of the damage is related to various factors such as the depth of the epicenter and the distance between the epicenter. Earthquakes greater than magnitude 6 are of strong magnitude and can produce great destructive power.
Seismic distribution
According to statistics, more than 5 million earthquakes occur on the earth every year, that is, tens of thousands of times a day. Of these, the vast majority are too small or too far away for people to feel. There are about a dozen or twenty earthquakes that can really cause serious harm to human beings, and only one or two earthquakes that can cause particularly serious disasters.
Through the statistics of a large amount of data on historical earthquakes and current earthquakes, scientists have found that the occurrence of earthquakes is closely related to time and geographical location.
In a certain area, there are more earthquakes in a period of time, and the magnitude is large, which is called the seismic activity period; In another period, there are fewer earthquakes and smaller magnitudes, which is called the calm period of seismic activity. The seismic cycle of the eastern part of the mainland is generally longer than that of the west, with an active cycle of about 300 years in the east and about 100 to 200 years in the west.
Geographically, 85% of the world's earthquakes occur at plate boundaries. Seismic zones are areas where earthquakes are concentrated, and there are four major seismic zones in the world: Pacific Rim seismic belt, Eurasian seismic belt, mid-ocean ridge seismic activity zone and continental rift valley seismic activity zone. The continent is located between the Pacific Rim seismic zone and the Eurasian seismic zone, and is squeezed by the Pacific plate, the Indian plate and the Philippine Sea plate, and the seismic fault zone is very active.
Wenchuan earthquake site (picture from Tuworm.com)
The Tanlu Fault Zone, which stretches for more than 2,000 kilometers, is the most important source of seismic threat in the eastern region. There is a fault zone perpendicular to the Tanlu Fault Zone in North China, known as the Zhangjiakou-Bohai Fault Zone, which was the "culprit" of the 1976 Tangshan earthquake.
There are many fault zones in the western part of the mainland, most of which exist in and around the Qinghai-Tibet Plateau. The Altun Fault Zone and Haiyuan Fault in the north bring serious earthquake disasters to Tibet, Qinghai and surrounding Sichuan, Yunnan, Gansu and Xinjiang.
The study of the distribution of earthquakes in time and geographical location is of great significance for earthquake prevention and monitoring, and is an important source of basis for earthquake prevention and disaster reduction.
Earthquake prevention and disaster reduction
Although earthquakes are currently one of the disasters that cannot be avoided and accurately predicted, as long as the correct and scientific earthquake avoidance method is mastered, the loss and damage can also be minimized.
When an earthquake occurs, first of all, you must remain calm, do not panic, and quickly judge your location and vibration situation. Experts at home and abroad generally believe that avoiding danger in place during an earthquake and evacuating quickly after an earthquake are the basic criteria for emergency earthquake avoidance.
If you are on the first floor of a bungalow or building, and the outdoor is relatively open, you can strive to quickly run out of the outdoor shock absorption. If it is the second floor of the building or above, and the indoor shock absorption conditions and building quality are good, the first choice is indoor shock absorption, and avoid indoor toilets, storage rooms, bathrooms and other places with small bays and load-bearing walls or supports.
When hiding indoors, you should quickly lie down on the ground, curl up as much as possible, and lower the center of gravity of the body; Protect the head and neck with clothes, pillows, etc., and do not press the mouth and nose; Grasp firm objects around you to prevent falls or body displacement.
If you are buried or trapped in the ruins during an earthquake, you should take measures to help yourself in a timely manner according to local conditions. If part of the limb is buried but the hands can move, first use the hands to remove the debris on the head and chest to ensure smooth breathing. Then use the masonry, sticks or other hard objects available around you as much as possible to establish a stable living space to prevent further collapse during aftershocks.
Search and rescue personnelSearch and rescue people trapped in earthquakes (picture from Tuworm Network)
If there is living space inside the ruins, the body is able to move on its own, and should try to move towards a place where there is light or possibly water and food; If you are injured, you can tear the cloth strip from the clothing and bandage it in time to avoid excessive blood loss.
The most important thing is that after the earthquake is buried, special attention should be paid to preserving physical strength, hitting the pipe or wall with bricks, iron pipes and other objects, and then shouting for help after determining that there are people above.
The earthquake is sudden and the process is short. Therefore, only by scientifically understanding earthquakes and understanding earthquake knowledge can we better cope with and reduce the losses caused by disasters.
Source: China Earthquake Information Network, China Science News, The Paper
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