Abstract
A newly designed laser earth strainmeter has been installed in the observation vault of the Matsushiro Seismological Observatory in Nagano, and earth strains have been measured over several days. The record of the laser strainmeter was compared with the record of a quartz strainmeter of the Observatory. The laser strainmeter is a modified Michelson type corner-cube interferometer having a 25m long airtight pipe and a high resolution analogue system for recording displacement of the interference fringe.
The errors caused by a wavelength variation, by an analogue recording of the fringe displacement, by a fluctuation of the refractive index of the air and by other effects are estimated. As a result of the estimations, the accuracy of this instrument is confirmed to be about 2×10-9.
