(1) piezoelectric electromagnetic induction method: the components form an included angle of 60, and the monitoring results are directional.
(2) Pressure-volume method: 45 included angles are formed between the components, and the monitoring results are directional.
(3) Volume strain method: the monitoring results are non-directional.
2. List of in-situ stress monitoring stations by piezomagnetic induction method
As early as 1960s, Li Siguang introduced the method of piezomagnetic induction in-situ stress measurement, and Wang Zongjie took the lead in trial-production experiments, and Wang went to Daye Iron Mine for field test and research.
1966 After Xingtai earthquake, Li Siguang established the first geostress monitoring station in Yaoshan, Longyao County, Hebei Province. At first, it began to continuously monitor the relationship between the relative changes of ground stress and earthquakes. Subsequently, the Institute of Geomechanics cooperated with the Earthquake Geology Brigade of the Ministry of Geology to study and improve the instruments and equipment of piezomagnetic induction method, and carried out systematic indoor and outdoor experimental research, which made great progress in theory. In the following 40 years, the construction of piezomagnetic induced geostress station reached a climax in China, and the 1 10 piezomagnetic induced geostress observation station was built nationwide. Most of them were built before Li Siguang died in 197 1 year, and the rest were built before the Tangshan earthquake in 1976. Now only five stations are still in the state of in-situ stress. The above is mainly based on the information provided by Huang Xiangning's paper in 2006, excluding the in-situ stress observation and research station established by the Institute of Geomechanics for many years.
With regard to earthquake prediction, it is our common goal to break through the difficulties of earthquake prediction by using seismic geological work methods, which will be discussed in Chapter 8. There is still a lot of work to be done before, and the following will discuss the in-situ stress measurement problems that need to be solved at present and in the long run.