Coupling mechanisms and detection thresholds are discussed for ring laser gyroscope measurement of seismic rotation, and simultaneous records from a ring laser and a standard EARSS seismograph 230 km from an ML 5.3 seismic event are compared. Rotation dominates tilt and strain in modulating the Sagnac frequency, and microseisms are not significant. Power spectral densities 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 floors (− 160 dB, or order nanoradians per second, and − 130 dB, respectively). A seismic sideband of the Earth rotation spectrum is found. These ring laser signals have magnitudes consistent with the amplitude of the standard seismograph record.