Comparison of standard and ring laser rotational seismograms

Coupling mechanisms and detection thresholds are discussed for ring laser g yroscope measurement of seismic rotation, and simultaneous records from a r ing laser and a standard EARSS seismograph 230 km from an M-L 5.3 seismic e vent are compared. Rotation dominates tilt and strain in modulating the Sag nac frequency, and microseisms are not significant. Power spectral densitie s for the ring laser and for the seismograph signals are enhanced in the 0. 2- to 10-Hz range by up to 18 and 60 dB, respectively, over the noise floor s ( - 160 dB, of order nanoradians per second, and - 130 dB, respectively). A seismic sideband of the Earth rotation spectrum is found. These ring las er signals have magnitudes consistent with the amplitude of the standard se ismograph record.