Measurement of Rotational Events in Regions Prone to Seismicity: A Review

On the basis of the explanation of rotational seismology as an area of study, a modern approach to the seismic rotation in various continuum models is summarized. The aim of this chapter is to formulate the fundamental requirements for rotational seismometer. Consequently, a review of all existing technologies of rotational seismometers including mechanical, electrochemical, magnetohydrodynamical, as well as optical type solutions is discussed. The analysis of their parameters that considers technical requirements enforced by rotational seismology has indicated an optical instrument using a Sagnac interferometer as the best solution. Fibre-Optic System for Rotational Events & phenomena Monitoring (FOSREM) with its main parameters and features is described as an example of such solution. Moreover, the example of rotational events recorded in Książ observatory, Poland, using mechanical rotational seismometers and FOSREM is presented. There are data for M = 3.8 earthquake near Jarocin, Poland on the 2012.01.06 at 15:37:56 at a distance of about 200 km from Książ. Although the used devices have totally different designs, the results obtained using FOSREM and the results calculated by mechanical devices show compatibility in rotational signals

Development of Three-Axis Fibre-Optic Seismograph for Direct and Autonomous Monitoring of Rotational Events with Perspective of Historical Review

The paper presents historical perspective of fibre-optic seismographs designed and constructed at the Institute of Applied Physics at Military University of Technology, Poland based on the so-called minimum configuration of fibre-optic gyroscope. The briefly presented history, which originated in the 1998 by the system named GS-13P, laid solid foundations for the construction of a three-axis fibre-optic seismograph. The presented system meets all technical requirements of rotational seismology in terms of measurement parameters (measuring range from 10−8 rad/s to several rad/s and frequency from 0.01 Hz to 100 Hz) and utility features (mobility, autonomy, power independence, environmental stability). The presented device provides universal application both for research in engineering applications (high buildings, chimneys, wind towers) as well as in seismological research

Towards uniformity of rotational events recording : initial data from common test engaging more than 40 sensors including a wide number of fiber-optic rotational seismometers

Rotational seismology is one of the fastest developing fields of science nowadays with strongly recognized significance. Capability of monitoring rotational ground motions represents a crucial aspect of improving civil safety and efficiency of seismological data gathering. The correct sensing network selection is very important for reliable data acquisition. This paper presents initial data obtained during the international research study which has involved more than 40 various rotational sensors collected in one place. The key novelty of this experiment was the possibility to compare data gathered by completely different rotational sensors during artificially generated ground vibrations. Authors collected data by four interferometric optical fiber sensors, Fiber-Optic System for Rotational Events & Phenomena Monitoring (FOSREM), which are mobile rotational seismographs with a wide measuring range from 10⁻⁷ rad/s up to even few rad/s, sensitive only to the rotational component of the ground movement. Presented experimental results show that FOSREMs are competitive in rotational events recording compared with the state-of-the-art rotational sensors but their operation still should be improved

Investigation of rotational motion in a reinforced concrete frame construction by a fiber optic gyroscope

This paper deals with an issue of a rotational motion impact on a construction and presents civil engineering applications of a fiber optic rotational seismograph named Fiber-Optic System for Rotational Events & Phenomena Monitoring. It has been designed for a long- term building monitoring and structural rotations’ recording. It is based on the Sagnac effect which enables to detect one-axis rotational motion in a direct way and without any reference system. It enables to detect a rotation component in the wide range of a signal amplitude from 10-8 rad/s to 10 rad/s, as well as a frequency from DC to 1000 Hz. Data presented in this paper show the behavior of a reinforced concrete frame construction on different floors. Several measurements were carried out by placing the applied sensor on different floor levels of a building. The laboratory and in-situ measurements confirmed that Fiber-Optic System for Rotational Events & Phenomena Monitoring is an accurate and suitable device for applications in civil engineering

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 Książ Castle, Poland, as well as in the coalmine “Ignacy” in Rybnik, Poland were also presented and analysed

Post-Processing of Raw Data Recorded Continuously Using a FORS—Fibre-Optic Rotational Seismograph

Modern optoelectronic devices use the advantage of digital systems for data processing aimed at delivering reliable information. However, since commonly used DACs have limited accuracy, some artefacts can be observed in data streams, especially in systems designed for continuous, long-term process monitoring. In this paper, the authors’ experience with data enhancement using a fibre-optic rotational seismograph (FORS) operating in a closed-loop mode is presented and discussed. Generally, two kinds of enhancement are described. The first one uses suitable filtering techniques adequate for FORS noise investigation, as well as a suitable data resampling method for transmitted data file size reduction. The second one relates to the artefacts observed during data recording in real time. The recording starting point is triggered when the detected signal exceeds a middle signal level and, therefore, the existence of artefacts generally disturbs the recording process. Although the artefacts are easily recognised by human eyes even at first sight, their automatic elimination is not so easy. In this paper, the authors propose a new concept of signal filtering to solve the above problem

Fibre Optic System for Monitoring Rotational Seismic Phenomena

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