Fiber-optic vibration sensing—I: Rotation measurement technique and its seismological applications

Abstract

The seismic wavefield can be decomposed into three-component translational motions and three-component rotational motions. The rotation components contain important wavefield gradient information and are key elements of seismic wavefield reconstruction. Due to the lack of stable high-sensitivity rotational measuring instruments, the rotation component was often neglected in different seismological applications in the past. The fiber-optic rotational seismometer, breaking the dilemma of the lack of measuring instruments, is the first commercialized rotating seismometer. It is also the most promising device for direct seismic wave rotation measurement. The fiber-optic rotational seismometer is based on the Sagnac effect and relies on mature fiber-optic gyroscope technology to measure the rotation components of vibration. It has the advantage that pure photoelectric sensor unaffected by translational motions and can be made portable equipment based on high sensitivity and wideband rotation measurement, which is beneficial to the application and promotion of rotation measurement. Therefore, the fiber-optic rotational seismograph and the traditional seismograph will complement each other to observe the six-component (6C) rotational and translational motions, which can extract seismic wavefield characteristics better, and can improve the performance of vibration monitoring, as well as the researches or applications on the seismic source rupture inversion, underground structure imaging and seismic damage mechanism. This article mainly introduces the basic principles of fiber-optic rotation measurement, the application of rotational seismology and its potential prospects.

Keywords

• rotational and translational motions
• rotation measurement
• fiber-optic vibration sensing
• fiber-optic rotational seismometer
• rotational seismology