In this paper, the history of china volume borehole deformation observation is introduced. The Chinese volume-strain product named model TJ-2, has the features of highest resolution, linearity and long time stability. And the principle, transducer structure, technical specifications, install method, data acquisition, and network communication technique etc. are introduced in this paper. The observation locations and earth-quake precursor application in china are also described.
A key observational requirement in the study of earthquakes is to observe deformation. The borehole deformation instrument is a very important observational tool. China's earthquake precursor observation strain used in drilling equipment, begun in 1966 (Chen 1995), has already had 40 years of history. The low-pressure magnetic sensitivity of borehole stress apparatus was used during 1966–1983. The volume type strain called TJ-1 instruments had been used successfully in 1983 (Su 1997,1985), and now is called TJ-2. At first, this high sensitivity instrument was not installed more until 2003 and only 31 units installed, mainly in northern China. In 2006, more are installed, although the country has already about 100 sets. In this paper, the TJ-2 principle, transducer structure, technical specifications, install method, data acquisition and network communication technique are introduced. In addition, its observation location and earthquake precursor application in china are also described.
China's TJ2 sensor principle is basically the same as that in the United States and Japan.
TJ-2 sensor installation diagram is shown in Figure 2. Firstly we used the special device to put the special cement into the bottom of the borehole, and then placed sensors on it. The purpose of this installation is to coupling the sensor with the borehole to keep consolidation of cement (Su 2004).