Installation of a high-sensitivity laser strainmeter in a tunnel in central Italy

A new laser interferometer for geophysical purposes is being operated in an underground laboratory in central Italy. A simple electro-optical technique has been used to limit the costs. The main characteristics of this instrument are: high sensitivity (Delta l/l approximate to 10(-12)), fast sampling rate (up to 6 kHz), large dynamic range (unbounded in principle), the capability of following strain rates as high as 7x10(-5) s(-1), and good reliability (two failures in nearly two years). (C) 1997 American Institute of Physics.