At 23:59 on December 18, a 6.2-magnitude earthquake occurred in Jishishan County, Linxia Hui Autonomous Prefecture, Gansu Province. So far, the earthquake has killed more than 100 people in Gansu and Qinghai.
Xu Xiwei, founding president of the National Institute of Natural Disaster Prevention and Control and professor of China University of Geosciences, believes that the southeast area of Gannan is located on the eastern edge of the Qinghai-Tibet Plateau and belongs to the north-south seismic zone.
According to the research and analysis of experts organized by the China Earthquake Network Center, the earthquake was located in the southeast of Gansu, about 3 kilometers away from the fault on the northern margin of the nearest fault, Lazhi Mountain. The preliminary results of the focal mechanism solution show that the earthquake is a thrust rupture.
What is a reverse fault earthquake?What was the surrounding earthquake situation before?How to reduce the damage of earthquakes?Read this article↓
▍What is a reverse fault earthquake? The Wenchuan earthquake also belongs to this category
Before we get to know about reverse faults, let's first understand what faults are.
A fault, as the name suggests, is a disconnected face.
What's broken? The rocks beneath our feet.
The rock is fractured by force, and the side of the fracture is the fault.
The intuitive phenomenon of fault movement is that the rocks on both sides will move relatively, and the scale of fault fault may be only a few centimeters, and the large one can reach thousands of kilometers or even thousands of meters.
According to the direction of movement, we divide faults into normal faults, reverse faults, and strike-slip faults.
Normal Fault: A dip-slip fault in which the block above the fault moves relatively downward. This type of fault occurs under the action of tensile forces.
Reverse Fault: A block above a fault moves relatively upward. This type of fault is common in extruded areas. For example, an area where one plate is subducted by another.
Strike-slip fault: Two blocks move horizontally.
Thrust fault is a kind of low-angle reverse fault, with a small dip angle and a large horizontal displacement.
Compared with strike-slip and normal fault earthquakes, thrust earthquakes have a stronger surface effect, and the 8.0 magnitude earthquake in Wenchuan, Sichuan Province in 2008 occurred on an onshore reverse fault. The Wenchuan earthquake is one of the world's largest intraplate thrust earthquakes that has occurred since instrumental records, and is an activity in the Longmenshan fault zone on the eastern edge of the Tibetan Plateau.
Why is the seismic activity in and around the Tibetan Plateau so violent? The main driving force is the squeezing of the Eurasian plate by the Indian Ocean plate, which on the one hand caused the uplift of the Tibetan Plateau, and on the other hand, it has brought tremendous pressure on the internal and surrounding blocks of the Tibetan Plateau. When the friction on the fault cannot withstand the pressure, dislocation occurs, causing an earthquake.
▍What about the surrounding historical earthquakes?
The magnitude 6.2 earthquake occurred in Jishishan County, Linxia Prefecture, Gansu Province (35.7 degrees north latitude, 102.79 degrees east longitude), with an epicenter depth of 10 kilometers.
As of 10 o'clock on the 19th, a total of 9 aftershocks of magnitude 3.0 and above were recorded in this earthquake, including 7 earthquakes of magnitude 3.0-3.9, 2 earthquakes of magnitude 4.0 or above, and the largest was an earthquake of magnitude 4.1 that occurred at 0:59 on the 19th.
In addition to this earthquake and aftershocks, since December, there have been three earthquakes of magnitude 3 or higher in Gansu, all of which occurred in Jiuquan City, with a maximum magnitude of 5.0.
According to the China Earthquake Network Quick Report Directory, there have been 24 earthquakes of magnitude 3 or higher in the past five years within 200 kilometers of the epicenter of the earthquake in Jishishan County, Linxia Prefecture, Gansu Province, and the largest earthquake is this earthquake.
Since 1900, there have been seven earthquakes of magnitude 5 or higher within 100 kilometers of the adjacent area of the earthquake, the most recent earthquake of magnitude 5 or higher was the 5.7 magnitude earthquake in Xiahe County on October 28, 2019, about 72 kilometers away from this earthquake, and the largest earthquake within 100 kilometers around the epicenter was the 6.7 magnitude earthquake in Kangle County on February 7, 1936.
In addition, according to the data of the Linxia Prefecture Bureau of Statistics, the registered population of Linxia Prefecture is 2.4485 million, and after preliminary calculation, the permanent population of Linxia Prefecture at the end of 2022 will be 2.124 million. Among them, the urban population is 828,700, the rural population is 1,295,300, and there are 42 ethnic groups, including Hui, Han, Dongxiang, Baoan, and Sala.
According to the website of the People's Government of Linxia Hui Autonomous Prefecture, Linxia Prefecture has a total area of 8,169 square kilometers, located in the upper reaches of the Yellow River, southwest of central Gansu Province, and is located in the transition zone from the Loess Plateau to the Qinghai-Tibet Plateau. The terrain in the state is complex, the river valley is vertical and horizontal, the hills are undulating, the altitude is between 1563~4585 meters, and the average altitude is 2000 meters.
The average elevation within 5 kilometers of the epicenter of the earthquake is about 2,787 meters. Xu Xiwei believes that the reasons for the heavy casualties caused by the 6.2 magnitude earthquake in Jishishan County, Linxia Prefecture, Gansu Province come from many aspects, such as poor seismic performance of houses, relatively dense population in the earthquake area, and people are in a state of rest late at night and have no time to take refuge.
▍In the event of an earthquake, do you run or hide, and what can you do to reduce the damage of earthquakes?
After a destructive earthquake occurs, do not panic, keep a cool head, and judge the distance and magnitude of the earthquake according to the shaking situation in time. Whether to run out of the outdoors or indoors to avoid shocks, you need to make a decision to ensure safety based on the environment you are in, and act decisively.
Body parts that need to be protected when absorbing shocks:
(1) Protect the head and neck: bow your head, protect the head or back of your neck with your hands, and if possible, use the items around you such as school bags, bedding, sofa cushions, etc. on your head.
(2) Protect your eyes: lower your head and close your eyes to prevent foreign objects from invading.
(3) Protect your mouth and nose: If possible, cover your mouth and nose with a wet towel to prevent dust and poisonous gas from being inhaled.
(4) Protect the body: try to curl up the body to lower the center of gravity of the body, and at the same time, firmly grasp the firm objects around you with both hands to prevent injuries from falling or being exposed to objects due to uncontrolled displacement of the body.
What should I do if I am buried after an earthquake?
If you are unfortunately buried in the rubble after the earthquake, try to stay calm and build up the confidence to survive. After the earthquake, aftershocks will continue to occur, and the environment may deteriorate further, so we should try to improve our environment and try to get out of danger.
The earthquake warning function enables specific operations
A devastating earthquake takes only about 12 seconds on average from the time a person feels the vibration to when a building is destroyed. Citizens can set up and turn on the earthquake mobile phone warning on their mobile phones in time to get the latest earthquake information or the best time to save themselves.
(1) Huawei: Set → security → emergency warning notifications → earthquake warnings
(2) Xiaomi: mobile phone manager→ family care→ earthquake early warning
(3) Honor: Set up → safety → emergency warning notification → earthquake early warning
(4) OPPO/OnePlus/Realme: Set → Security → SOS Emergency Contact→ Natural Disaster Alert→ Earthquake Alert
(5) vivo/iQOO: Set → earthquake early warning → enable earthquake early warning service → the weather app
(6) Apple/Samsung/other mobile phones: search for the keyword "earthquake warning" and download the relevant app by yourself
(★ Tips: Remember to help your family also turn on the earthquake warning function)
(▼Huawei phone example)
Peace be upon you!
(Yangcheng Evening News • Yangcheng Pai Comprehensive Jishishan County 6.2 Earthquake Press Conference, National Earthquake Science Data Center, China Earthquake Network, China Science News, Linxia Hui Autonomous Prefecture People's Government Website, Linxia Prefecture Bureau of Statistics, Xinhua News Agency, CCTV News, China News Network, Sichuan Earthquake Bureau, Nanyue Earthquake Prevention and Disaster Reduction WeChat Public Account, @人民日报等)
Topic moderator | Reporter Chen Shijie
Editor: Chen Shijie
Source: Yangcheng Evening News • Yangcheng faction