Abstract Tests for observing strain changes in soil with borehole strainmeters are needed in researches of earthquake forecast as well as geodynamics. The observation can be testified if solid earth tides will be clearly recognized. The difference of observation in soil from in rocks lies on the looseness of the medium. Therefore, the strainmeter should be placed significantly deeper in order to solve the problem of permanent deformation. Meanwhile, since soil responds elastically to small dynamic deformation, and the tides of strain are on the order of
10-8, the placement may not be necessarily very deep. Results of theoretic analysis indicate that, although resolution of borehole strainmeter for observation in soil is lower than in rocks, soil deforms much larger than rocks for same stress changes will benefit the observation of tides in soil. Existence of pore liquid will bring about disturbance to borehole strain observation and the sensor should be placed beyond the depth close to water table. It will eventually be checked through practical tests.Whether the present borehole strainmeters can record earth tides.
