Detecting the rotation of the earth's surface and capturing volcanic and seismic activity
A gyroscope is a device specifically designed to measure changes in direction or angular velocity. In order to further study the phenomenon of seismic wave rotation caused by earthquakes or volcanic activity, researchers have developed a fiber optic gyroscope based on the Sagnac effect. The Sagnac effect refers to the fact that when two beams of light pass around a rotating object in opposite directions on the same closed route, the two beams of light will show different phase changes, resulting in the movement of interference fringes on the screen. The rotation rate determines the interference pattern, so the angular velocity of the material's rotation can be detected by measuring the interference fringes.
The researchers assembled a three-axis fiber optic gyroscope using standard laboratory instruments and components to measure the three directions of rotational motion. In order to be able to test the performance of the fiber optic gyroscope on each axis, they input light into a 2 km long fiber optic cable, which forms a continuous loop with input and output connections and is precisely wound on a 25 cm diameter aluminum spool to form a coil, and placed the optical gyroscope in a controlled laboratory environment on top of the crater. "Our laboratory is located in the heart of an active volcanic area, forming a natural source of earthquakes," said Avino. "We experience small and medium earthquakes almost every day, so we can measure and obtain a lot of ground rotation data, which can be continuously analyzed to study seismic and volcanic phenomena in the Campi Flegrei area."
Figure 2 Earthquake signal monitored by fiber optic gyroscope
After 5 months of measurement and analysis, the gyroscope detected seismic noise and ground rotation wave fields caused by small to medium-sized local earthquakes (MD<3), and showed a sensitivity of 5×10-7 - 8×10-9rad/s/ in a frequency bandwidth of 5 mHz-50 Hz. "The first version of the system showed a resolution comparable to other state-of-the-art fiber gyroscopes," said Marialuisa Capezzuto, the first author of the paper. "It has a very good duty cycle (the percentage of time the instrument measures and collects data), which allowed us to operate the system continuously for about five months."
Improving gyroscope performance and opening a new chapter of future precision observation
Through careful characterization, the fiber optic gyroscope has shown performance comparable to that of fiber optic gyroscopes currently used for seismic measurements. In future plans, researchers will also further improve the sensitivity and long-term stability of fiber optic gyroscopes by experimenting with more symmetrical optical devices and active temperature stabilization, so as to achieve permanent, stable, and highly sensitive observation of volcanic and earthquake rotational motion.
Highly sensitive gyroscopes will bring revolutionary changes to the monitoring and early warning of natural disasters such as volcanoes and earthquakes, significantly improve our ability to perceive crustal activity, achieve all-weather, uninterrupted monitoring, ensure that disasters can be quickly captured and warned before they occur, greatly improve disaster prevention capabilities, and protect people's lives and property. At the same time, the application of gyroscopes will also promote the development of earthquake science research to a deeper level and make new contributions to human understanding and protection of the earth.
