Shulou(Shulou.com)11/24 Report--

Almost every time after an earthquake that has a great impact on society, the term "mobile earthquake early warning" appears in front of the public. What is earthquake warning? What is the principle of earthquake early warning? What kind of process did we go through from the earthquake to the time we received the notification on our mobile phone?

Part.01, distinguishing between earthquake early warning and earthquake prediction earthquake early warning uses the principle that radio waves propagate faster than seismic waves to warn early warning targets after an earthquake occurs and before the earthquake wave reaches a certain area, so as to minimize casualties.

"Forecast" refers to advance notices that have not yet occurred but may occur, such as the weather forecast for high probability of rain tomorrow. We cannot give a definite answer in advance whether it will rain tomorrow. It is affected by many factors, so it is a probabilistic event. Earthquake prediction is different from weather prediction, which has the principle of "uncertainty and non-notification", that is, it is necessary to consider social credibility. If the authorities make mistakes in earthquake prediction for many times, it will have a negative impact on the public.

The power to issue earthquake prediction in China is vested in governments at or above the provincial level. According to Article 29 of the Law of the people's Republic of China on earthquake Prevention and disaster reduction, the state implements a unified system of issuing opinions on earthquake prediction. Opinions on long-term and medium-term earthquake prediction nationwide shall be issued by the State Council. Opinions on earthquake prediction within the administrative areas of provinces, autonomous regions and municipalities directly under the Central Government shall be issued by the people's governments of provinces, autonomous regions and municipalities directly under the Central Government in accordance with the procedures prescribed by the State Council. Except for publishing the research results of himself or his unit on the long-term and medium-term seismicity trends and conducting relevant academic exchanges, no unit or individual may disseminate earthquake prediction opinions to the public. No unit or individual may disseminate to the public opinions on earthquake prediction and their evaluation results. At present, from a worldwide point of view, earthquake prediction is still an unsolved problem, so the more reliable earthquake prevention measure is earthquake early warning.

Part.02, the principle of earthquake early warning the propagation of radio waves is much faster than that of seismic waves, and the propagation speeds of different types of seismic waves are different. People can use these time differences to achieve earthquake early warning. After an earthquake, the released energy propagates underground in the form of seismic waves, including longitudinal and shear waves. Because the longitudinal wave produced by the earthquake propagates faster than the shear wave with stronger destructive power, it can be the first to reach the ground to "tip off" the early warning system. At the same time, it takes time for the earthquake to spread from the source to a certain area (that is, the ratio of the propagation distance to the seismic wave velocity). People can use this time difference to race with the earthquake to achieve early warning. When the earthquake monitoring station detects the first arrival P wave (P wave), the system will send an alarm after processing the information. The projection point of the source on the earth's surface is called the epicenter, and the spherical distance from a certain point to the epicenter is the epicenter distance. Therefore, in general, the larger the epicenter distance, the longer the early warning time. The earthquake that occurred in Pingyuan County, Dezhou City, Shandong Province on August 6 made the earthquake felt obviously in many areas, including Beijing, Tianjin, Shijiazhuang, Taiyuan, Zhengzhou and so on. The early warning time varies from a few seconds to dozens of seconds from the epicenter (figure 2).

Fig. 2 earthquake early warning App page although it is difficult for ordinary people to take effective escape methods within more than ten seconds, and may even cause injury because of panic, early warning buys the public time for emergency treatment and escape. This also inspires us that we should actively understand the earthquake response measures at ordinary times, such as ① looking for a suitable hiding position, such as the corner of the load-bearing wall or a small room forming a triangular area; ② protects the head to avoid lying position; ③ turns off the power of open fire and forbids taking elevators; ④ uses pipes such as water pipes or radiators to knock for help, avoiding shouting to save energy.

The whole process of earthquake early warning realized by Part.03 and mobile phone "earthquake early warning" by mobile phone refers to the function of receiving earthquake early warning information through mobile phone equipment and transmitting it to the user in time to inform the user in advance of the occurrence of earthquake. It makes comprehensive use of a variety of technical means, such as earthquake sensor, data transmission system, earthquake early warning analysis system and so on (figure 3).

① seismic sensor is a kind of equipment which can sense seismic vibration. Accelerometer is usually used to measure the intensity of seismic wave. When the seismic sensor detects the propagation of seismic waves, it will send the trigger signal to the data center through data transmission. The monitoring stations distributed in different geographical locations use seismic sensors to monitor seismic activity in real time to form an earthquake detection network.

The ② data transmission system is responsible for transmitting the monitored seismic data from the earthquake monitoring station to the data center. This process is usually realized by wireless communication technology, such as mobile communication network, satellite communication, etc., to ensure the real-time transmission and accuracy of data.

The ③ earthquake early warning analysis system carries out real-time analysis and processing according to the data transmitted by the earthquake monitoring network to determine the magnitude, source and expected range of influence of the earthquake. When the earthquake early warning analysis system is confirmed, the early warning information is transmitted to the corresponding mobile phone and other user terminals.

Fig. 3 earthquake early warning process (source: Chengdu Hi-tech disaster reduction Research Station website) the mobile phone can not only act as a signal receiver in earthquake early warning and passively receive early warning information sent by earthquake monitoring stations, it can also be used as an earthquake monitor. In order to further reduce the blind area of early warning and improve the efficiency of early warning, more researchers have begun to try to replace the target of traditional early warning receiving instruments with built-in sensors. By using built-in seismic sensors and other sensors to detect seismic waves, the phone can perform local calculation to determine seismic signals when sensing vibration signals. The number of mobile phones far exceeds the number of earthquake monitoring instruments currently installed, which can improve the coverage and accuracy of the early warning network and effectively solve the problem of blind areas of early warning. At the same time, it has strong expansibility and low operating cost, so it can effectively improve the ability of earthquake prevention and disaster reduction.

The "earthquake early warning" function of mobile phone is based on the earthquake early warning system, which can realize real-time monitoring and early warning of earthquakes. The realization of this function enables users to obtain earthquake early warning information in time, so as to take corresponding prevention and protection measures. It is believed that with the continuous progress of science and technology, the development of "earthquake early warning" function of mobile phone will play an important role in earthquake disaster prevention and disaster reduction in the future.

This article is from the official account of Wechat: stone popular Science Studio (ID:Dr__Stone), by KF

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