Interpretation | Sichuan Changning earthquake, Chengdu issued a 61-second advance warning, how did it do it?
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Earthquakes can provide early warning, and early warning can save lives.
Text | I/O
If the warning time is 3 seconds, the casualty rate can be reduced by 14%; if the warning time is 10 seconds and 60 seconds, the casualties can be reduced by 39% and 95%.
The above is the relevant research data on earthquake early warning in reducing casualties. In the 6.0-magnitude earthquake that occurred in Changning County, Yibin, Sichuan at 22:55 on June 17, the earthquake early warning network issued a warning to Yibin 10 seconds in advance and to Chengdu 61 seconds in advance, winning precious time for the people in the earthquake-stricken areas and gaining praise on Weibo and other channels.
In fact, earthquake early warning is not the same as earthquake prediction.
Leifeng.com learned that earthquake forecast is the advance notification of an earthquake that has not yet occurred but is likely to occur; earthquake warning refers to the issuance of an alarm a few seconds to tens of seconds in advance after an earthquake occurs, before the seismic waves spread to the fortified area, in order to inform local people to take emergency measures and minimize casualties.
To understand the mechanism of earthquake early warning, we need to first understand how seismic waves are transmitted.
There are two types of seismic waves that propagate inside the earth's crust. One is a faster but less destructive longitudinal wave, which propagates in the earth's crust at a speed of about 5.5 km/s to 7 km/s. The other is a more destructive transverse wave, which is the main cause of the damage caused by earthquakes to the surface. The propagation speed of transverse waves is slower, at 3.2 km/s to 4 km/s. When an earthquake occurs, the seismic monitor near the epicenter first captures the longitudinal wave signal and transmits the data to the early warning center. When the information from 2 to 3 stations is summarized, the early warning center will analyze these signals and issue the first warning.
Since the propagation speed of radio waves is much faster than the 300,000 km/s of seismic waves, warning information can be sent to areas that will be affected by the earthquake through terminals such as smartphones, radio and television, Weibo, and earthquake warning information receiving servers before damage is caused, thereby using a time difference of several seconds to tens of seconds to reduce casualties and losses.
In the 6.0 magnitude earthquake in Changning, Yibin, Sichuan Xichang Junbo Foreign Language School received an early warning 60 seconds in advance, and more than 4,000 teachers and students were successfully evacuated outdoors; the director of the school's political and educational department said that they heard the alarm when they were going to bed, and then all the teachers and students in the school quickly evacuated to a safe place, and no one was injured.
In this regard, Wang Tun, director of the Chengdu High-tech Disaster Reduction Research Institute, also introduced:
The principle of earthquake early warning is to use the fact that radio waves are faster than seismic waves. When an earthquake begins to occur at the epicenter, the earthquake early warning network can monitor and issue an alarm several to tens of seconds in advance to areas that have not yet been affected by the earthquake.
It should be noted that this is not the first time that the earthquake early warning function provided in the 6.0-magnitude Changning earthquake has been used.
At 21:19 on August 8, 2017, a magnitude 7.0 earthquake occurred in Jiuzhaigou County, Aba Prefecture, Sichuan Province, with a focal depth of 20 kilometers. Almost at the same time as the Jiuzhaigou earthquake occurred, an app called Earthquake Early Warning (ICL) released 5 consecutive push notifications in less than 20 seconds, providing early warning information to users in Chengdu 71 seconds in advance; Wenchuan residents also received earthquake early warning information in a timely manner through the earthquake countdown that appeared on TV.
The research and development team behind this early warning system is none other than the Chengdu Hi-Tech Disaster Reduction Institute (Institute of Care-Life, ICL for short).
Public information shows that the Chengdu High-tech Disaster Reduction Research Institute was established after the 5.12 Wenchuan earthquake. It was founded by Dr. Wang Tun, a talent of the National Thousand Talents Plan, and took the lead in establishing the Sichuan Key Laboratory of Earthquake Early Warning, which was authorized by the Sichuan Provincial Government. The Institute of Disaster Reduction and the Key Laboratory are committed to the research and development of earthquake early warning technology, transformation of results and application.
Leifeng.com found that the earthquake early warning system is mainly divided into four links: earthquake monitoring, early warning information analysis and processing, early warning information release, early warning information reception and application. Specifically, a high-density network of stations is deployed in earthquake-prone areas to monitor earthquakes. The monitors send the key information of the monitored seismic motion to the early warning center for analysis and processing. The early warning center then releases the early warning information, and users receive the early warning information and take risk avoidance and emergency measures.
The ICL earthquake early warning system, which played a role in the 6.0-magnitude earthquake in Changning, Yibin, has been publicly tested by tens of thousands of actual earthquakes. In particular, it has successfully warned 50 earthquakes that caused damage, including the 7-magnitude Lushan earthquake, the 6.5-magnitude Ludian earthquake in Yunnan, the 6.3-magnitude Kangding earthquake in Sichuan, and the 7-magnitude Jiuzhaigou earthquake, without false alarms. The early warning system has achieved the simultaneous release of early warning information through smartphones, radio and television, Weibo, and earthquake early warning information receiving servers, making my country the third country with earthquake early warning technology capabilities after Mexico and Japan, and making my country's earthquake early warning technology at the world's leading level.
At present, the Chengdu High-tech Disaster Reduction Research Institute has jointly built the world's largest earthquake early warning network with the earthquake prevention and disaster reduction departments (earthquake departments) of cities and counties across the country, extending to 31 provinces (municipalities and autonomous regions), covering an area of 2.2 million square kilometers and covering 90% of the population in my country's earthquake-prone areas (660 million people).
However, according to Global Science, an embarrassing problem is that the early warning system can provide early warnings for surrounding areas, but it is powerless to the epicenter area that is most severely damaged. Since the formation of early warnings requires seismic waves to reach at least two stations tens of kilometers away, at this time, the damage caused by shear waves to the epicenter has already occurred, which is the so-called "early warning blind spot."
At present, the minimum range of ICL's early warning blind zone is a circle with the epicenter as the center and a radius of 21 kilometers. This range is equivalent to the area with the greatest damage in a magnitude 7 earthquake. The scope of the early warning blind zone can be reduced by improving the density of the station network, the quality of observation data, and the real-time transmission and processing of data, but for residents in the epicenter area, the early warning will always come too late.
Of course, the realization of the earthquake early warning network is not only the credit of the Chengdu High-tech Disaster Reduction Research Institute, it is also inseparable from the support of various early warning channels such as radio and television, Internet TV platforms and offline residential communities.
Leifeng.com found that on May 28, 2019, Chengdu High-tech Disaster Reduction Research Institute also signed a deepening cooperation agreement with Sichuan Cable Radio and Television Network Co., Ltd. and Chengdu High-tech Disaster Reduction Research Institute for the "last mile" of earthquake early warning reception to promote the "last mile" of earthquake early warning reception.
At that time, the two sides announced that the television earthquake early warning would be extended to all 13 cities and prefectures in all earthquake zones in Sichuan, covering 79 districts and counties, accounting for 60% of the districts and counties in the earthquake zones in Sichuan Province. Among them, Guangyuan, Leshan, Yibin, Liangshan, Deyang, Ya'an and other cities and prefectures have been fully authorized to open, and some districts and counties in another 7 cities and prefectures have been authorized to open. This will ensure that when the next major earthquake occurs, televisions with built-in earthquake early warning services will issue warnings in areas authorized by local governments at all levels, and warn users before the earthquake affects them, thereby reducing casualties.
Of course, in addition to TV warnings and offline channels, the Chengdu High-tech Disaster Reduction Research Institute has also launched its own mobile app - Earthquake Warning, which says "Earthquakes can be warned, and warnings can save lives", and it is completely free. Leifeng.com learned that due to various reasons, the download volume and usage of this app are not high, so the update frequency is not high. The last update was 3 years ago; however, the app has built-in earthquake lists, earthquake distribution, earthquake science popularization and other functions, which can all be used normally.
It is worth mentioning that after the 6.0 magnitude earthquake in Changning, Yibin, the number of downloads of the Earthquake Early Warning App has continued to rise - it has now ranked first on the App Atore free list.
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