Abstract
For many years, seismological research mainly focuses on translational ground motions due to the lack of appropriate sensors. However, because of the development of devices based on Sagnac effect, measuring rotational waves directly comes available. In this work, a portable three-component broadband rotational seismometer named RotSensor3C based on open loop interferometric fiber optic gyroscope (IFOG) is designed and demonstrated. Laboratory tests and results are illustrated in detail. The self-noise ranging from 0.005 Hz to 125 Hz is about , and with the harmonics compensation the scale factor variation over is lower than 10 ppm (parts per million). The misalignment matrix method is adopted to revise the output rotation rate. In a special near field experiment using the explosive source, the back-azimuths and phase velocity are estimated by the recorded acceleration and rotation rate. All the results prove the practicability of this new rotational sensor.
Highlights
The rotational effects in the great earthquakes attract researchers to develop seismological theory and find out the physical nature of seismic waves
The effects of rotational motions are still ignored in modern observational seismology, as the results of the difficulties in measuring rotational motions and the widespread belief that they are insignificant [2]
Because of the development of devices based on Sagnac effect, measuring rotational seismic waves directly becomes available, and these sensors display a lower flat frequency range for measurement [4]
Summary
The rotational effects in the great earthquakes attract researchers to develop seismological theory and find out the physical nature of seismic waves. The common approaches to observe rotations include mechanical devices, seismic arrays, IFOGs and ring laser gyroscopes (RLGs). According to their measurement characteristics, they can be divided into two groups of sensors. Comparing with the first group of sensors, these two kinds of optical devices are completely insensitive to translational motion and able to measure rotational motions directly [11]. They are more accurate, making them the perfect candidates for the measurement of strong motion.
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