Softhis (Poland)

Rotational Seismology caused highly interest in investigation of rotational movements generated by earthquake, mines and existing in engineering structures. The most oppressive aspect of research in this field is technical requirements for sensors. However, the instruments basing on the Sagnac effect seem to be the most appropriate to investigate rotational effects due to the fact that they are entirely insensitive to translational motion and are able to measure rotation rate in wide frequency and amplitude band. The paper presents a new device FOSREM which, based on FOG, possesses special solutions that makes it perfect, in author knowledge, for any rotation sensing.

ABSTRACT In this article we show a fibre-optic device base d on the Sagnac effect designed for measuring rotational motions which appear during seismic events. The experimental investigation s of presented Autonomous Fibe r-Optical Rotational Seismograph s indicate that such device s keep the accuracy no less than  -9 WR  -8 rad/s in the frequ ency band from 0.83 Hz to 106.15 Hz. Furthermore , the ir operations are controlled fully remotely via Internet. W e present the comparison of results obtained by such system in the field test with a mechanical rotational seismo meter which is mounted simultan eously in the seism ological observatory LQ.VL*3RODQG Keywords : fibre optic sensor ; rotational seismograph ; seismic events; remote control ; Internet 1. INTRODUCTION The observations of strange, rotational deformations of buildings after earthquakes lead to enlargement of interest in seismic rotational phenomena 1

We outline the development and the application in a field test of the Autonomous Fibre-Optic Rotational Seismograph (AFORS), which utilizes the Sagnac effect for a direct measurement of the seismic-origin rotations of the ground. The main advantage of AFORS is its complete insensitivity to linear motions, as well as a direct measurement of rotational components emitted during seismic events. The presented system contains a special autonomous signal processing unit which optimizes its operation for the measurement of rotation motions, whereas the applied telemetric system based on the Internet allows for an AFORS remote control. The laboratory investigation of such two devices indicated that they keep an accuracy of no less than 5.1 × 10−9 to 5.5 × 10−8 rad/s in the detection frequency band from 0.83∼106.15 Hz and protect linear changes of sensitivity in the above bandpass. Some experimental results of an AFORS-1 application for a continuous monitoring of the rotational events in the Książ (Poland) seismological observatory are also presented.