A test performance of optical fibre sensors for real-time investigations of rotational seismic events: a case study in laboratory and field conditions

Preliminary results of laboratory and field tests of fibre optic rotational seismographs designed for rotational seismology are presented. In order to meet new directions of the research in this field, there is clearly a great need for suitable and extremely sensitive wideband sensors. The presented rotational seismographs based on the fibre optic gyroscopes show significant advantages over other sensor technologies when used in the seismological applications. Although the presented results are prepared for systems designed to record strong events expected by the so-called "engineering seismology", the described system modification shows that it is possible to construct a device suitable for weak events monitoring expected by basic seismological research. The presented sensors are characterized, first and foremost, by a wide measuring range. They detect signals with amplitudes ranging from several dozen nrad/s up to even few rad/s and frequencies from 0.01 Hz to 100 Hz. The performed Allan variance analysis indicates the sensors main parameters: angle random walk in the range of 3 . 10(-8)-2.10(-7) rad/s and bias instability in the range of 2 . 10(-9)-2 . 10(-8) rad/s depending on the device. The results concerning the registration of rotational seismic events by the systems located in Ksiaz Castle, Poland, as well as in the coalmine "Ignacy" in Rybnik, Poland were also presented and analysed.