Researchers have developed a prototype fiber optic gyroscope to monitor the earth’s rotation during earthquakes at Campi Flegrei in Naples. This advanced sensor system, which captures rotational and linear movements, could contribute to better risk assessment and early warning systems in this volcanic region.
“When there is seismic activity, the Earth’s surface is subjected to both linear and rotational movements,” said research team leader Saverio Avino of the Consiglio Nazionale delle Ricerche Istituto Nazionale di Ottica. “Although spins are often very small and not generally monitored, the ability to capture them will provide a more comprehensive understanding of the Earth’s internal dynamics and the sources of seismic waves.”
The new rotation sensors, based on a 2 km fiber optic gyroscope, recorded data continuously for five months and successfully detected noise and ground rotation in small and medium-sized local earthquakes. The researchers published preliminary data from the sensor’s observations in the journal Optica Publishing Group. Applied Optics.
Deployment of sensors in Naples
Naples, home to approximately 3 million people and 3 active volcanoes, is equipped with a multi-parameter sensor network covering the entire city. These sensors monitor various physical and chemical parameters to study seismic and volcanic activity in real time.
“Measuring the Earth’s rotation would add another piece to this complex mosaic of sensors,” said Danilo Galuzzo of the National Institute of Geophysics and Volcanology. “This additional information will also help provide a comprehensive understanding of volcanic earthquake signals, which is critical for detecting any changes in volcanic dynamics.”
Measurement of rotational motion
Gyroscopes are devices used to detect and measure changes in direction or angular velocity (the rate at which an object rotates). For example, in smartphones, simple gyroscopes detect and measure the orientation and rotation of the device. To measure the spin of seismic waves resulting from an earthquake or volcanic activity, researchers developed a more complex gyroscope based on the Sagnac effect.
The Sagnac effect occurs when light traveling in opposite directions around a closed circuit exhibits different transit times. This results in measurable interference patterns in the light depending on the speed of the cycle. By measuring the interference of light, angular velocity can be determined with high resolution.
“Our laboratories are located in the center of an active volcanic region, thus creating a natural source of earthquakes,” Avino said. said. “As we experience small/moderate earthquakes almost every day, we are able to measure and obtain large amounts of ground rotation data that can be analyzed consistently to study the seismic and volcanic events of the Campi Flegrei region.”
Recording seismic activity
The researchers created a prototype fiber optic rotation sensor using standard laboratory equipment and components. To test this, they injected light into a 2-kilometer fiber optic cable similar to those used in optical telecommunications. The fiber optic cable created a loop where the input and output were connected, creating an uninterrupted, continuous light path, and was precisely wrapped around a 25 cm diameter aluminum coil to form the coil.
During the experiments, the optical sensor is stored in a controlled laboratory environment in a building located at the top of a volcano’s caldera, a large depression that forms when a volcano erupts and collapses. “This first version of the system demonstrated a resolution comparable to other state-of-the-art fiber optic gyroscopes,” said first author Marialuiza Capezzuto, who works at CNR-INO and worked on the experimental device. “It also had a very good duty cycle (the percentage of time the device was measuring/collecting data), which allowed us to run the system continuously for about five months.”
“The gyroscope prototype can measure only one of the three directional components of rotational motion. However, a combination of three identical gyroscopes, each oriented at a separate axis of rotation, can be used to capture all three components.” said Luigi Santamaria Amato from the Italian Space Agency (ASI). The researchers plan to make a three-axis gyroscope after improving the resolution and stability of the single-axis system. They eventually want to create a permanent observatory monitoring the rotation of the earth in the Campi Flegrei area.
Source: Port Altele
