According to the time of earthquake occurrence, the prediction can be divided into medium and long term prediction, short-term prediction and pre-earthquake prediction. Medium and long term prediction is mainly implemented through investigation and study of seismic and geological conditions: Short-term prediction depends not only on the investigation of earthquake and geological conditions but also various monitoring methods: Pre-earthquake prediction mainly depends on various monitoring means.
Seismic monitoring mainly utilize various instruments and equipment to study various physical changes occurring in rocks, seismograph records the weak seismic energy continuously, analysis and research records can infer the seismic trend. In addition, the abnormal reactions of weather and animals, the production of ground light and sound, are also the harbinger of the coming earthquake.
Earthquake prediction is still an unsolved problem for all mankind, and is still in the exploratory stage. China's earthquake monitoring and prediction started late. Following the 1966 Xingtai earthquake, the earthquake monitoring and forecasting system was gradually developed under the suggestion of Premier Zhou Enlai, China's earthquake workers successfully predicted the February 4, 1975 Haicheng earthquake of magnitude 7.3, which brought a great surprise to the earthquake monitoring and forecasting system, and even to the whole seismic system, called "miracle in the history of Seismology" by the world. But it failed to predict the Tangshan earthquake a year later, so the earthquake prediction is very difficult.
（1）Earthquake prediction is a worldwide problem
Human society has developed so far, humans can travel through space by plane or spacecraft and land on the moon 384, 000 km from earth: Distant planets can be directly observed using space telescopes. But inside the earth, only can active in a few meters deep underground mall, dozens of meters of facilities, thousands of meters of mines. People can retrieve rocks from the moon, but they can't get rocks tens of kilometers deep inside the earth. It may be said that heaven is easy to enter but earth is difficult.
Academician Chen Yuntai has systematically summarized and explained the main difficulties of earthquake prediction: “Impenetrability” of the earth's interior: “Non-frequency” occurrence of large earthquakes: Complexity of seismic physical processes.
Due to earthquakes are difficult to forecast, many countries do not pay much attention to earthquake forecasts. For example, most earthquakes in the United States occur in the mountains of the west coast, where the population is small and houses are built solidly as a major measure to mitigate the effects of earthquakes. Some countries have focused on establishing earthquake warning mechanisms, mainly utilize the time difference caused by the different propagation speed of the p-wave and s-wave in the earth's crust, and sends out the alarm after the earthquake, so as to gain precious time for people to avoid the danger. Because of time difference is usually only a few seconds to dozens of seconds, it can only help the relevant important departments to take emergency defensive measures before the seismic wave arrives at present, such as shutting down power stations and other lifeline projects. The system also requires higher accuracy of seismic monitoring, otherwise, interference factors such as lightning may cause the system to issue false alarms and have a great impact on social stability. Early warning system played a role in the Japan earthquake of magnitude 9 in 2011. According to relevant reports, after strong earthquake, earthquake warning system releases earthquake alerts through radio, television and satellite data transmission systems, normal TV broadcast was interrupted by loud alarms, some people who subscribe to special early-warning services can also receive alerts via mobile phones and e-mail.
(2) China's earthquake monitoring and prediction level
China's first seismological observatory was established in 1930 by the famous seismologist Shanbang Li, located in JiuFeng, Beijing. After more than half a century of struggle, china's seismostation has grown from one to several hundred, at present, it has a national basic network, a network for rapid information of major earthquakes, all of them can be recorded by seismograph and reported to the analysis and prediction center of China seismological bureau, making China's seismic observation technology in the forefront of the world.
The level and current situation of earthquake prediction in China can be generally summarized as the following sentences: Mechanism and laws of earthquake gestation are known, but not fully understood: certain types of earthquakes can be predicted to a certain extent, but most earthquakes cannot be predicted: Medium and long-term forecasting has certain credibility, but the success rate of short impending forecasting is still low.
Specifically, China has made the following progress in the exploration of earthquake prediction: Many precursory phenomena were obtained from the summary of a large number of earthquakes in different regions, a series of earthquake prediction experiences were summarized. At the same time, some forecasting experiences have been applied to some earthquake forecasting practices and have been successful. Criterion, index and method of earthquake prediction are studied deeply, and technical procedures for earthquake prediction, taking the study of earthquake prediction to practical one step further, forming a practical software for regional analysis and prediction. Some success has been achieved in the practice of earthquake prediction, especially in 1966 – 1976, Haicheng earthquake, Longling earthquake, Songpan Pingwu earthquake made better prediction, effectively mitigated disasters. Nevertheless, the current forecast level is still very low, in a short period of time, especially short impending forecast is still not possible to get by completely. However, through further monitoring and forecasting practice, and scientific research, especially short-term and imminent prediction work, it is possible to predict some destructive earthquakes before their occurrence.
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