Application of fibre-optic rotational seismometer in investigation of seismic rotational waves

Application of a fibre-optic Sagnac interferometer as a rotational seismometer is presented in this paper. It is a new device which parameters (sensitivity equal to 4.3×10⁻⁸ rad/s for 2σ) are comparable with the parameters of typical mechanical rotational seismometers. However, a direct measurement of rotation without influence of linear motions for fibre-optic rotational seismometer designed it for a direct measurement of a ground rotation component. Experimental data obtained during simultaneous application of the above two types of sensors are also presented. Research of near-field seismic events, the amplitude of which has been identified in the range of 1.5×10⁻⁶ rad/s to 2×10⁻⁷ rad/s, shows directly that, so-called, seismic rotational waves exist independently of typical seismic waves generated during earthquakes.