High-temperature borehole seismometer with fiber optic displacement sensor

A high-temperature, high sensitive borehole seismometer with fibre optic interferometric displacement sensors has been constructed and practically tested Its parameters are suited for monitoring of seismic vibrations at working temperatures from 20°C to 300°C. Long term stability of performance characteristics has been confirmed for the seismic receiver and the fibre optic components at elevated temperatures and for several km of fibre optic signal transmission lines. Seismic vibrations could be monitored by coupling the seismic mass via spherical reflectors to a single-mode fibre optic Michelson interferometer. Optical phase processing based on wavelength modulation of tuneable DFB laser source yields <0. 1nm sensitivity of seismic vibrations within 0.1. .30Hz information bandwidth. Laboratory test measurements at elevated temperatures agree well with the results of an electrodynamic seismometer.