1:45 PM - 3:15 PM
[STT42-P01] DAS Observations on the Fiber-Optical cables of JR Central and its Application to Seismological Research
Keywords:optic fiber sensing, DAS, train, ground motion
Since 2021, we have been conducting seismic observation by DAS using fiber-optic communication cables along the tracks of the Tokaido Shinkansen and the laid in Yamanashi Prefecture by JR Central. Our DAS observation started from a 5.8 km section of the Tokaido Shinkansen starting from Hamamatsu Station in January 2021(Yoshimi et al., JpGU, 2021). Then we made long-range and long-term observations along a 145 km section between Odawara Sta and Kakegawa Sta, with a DAS interrogator at Atami Sta or Shizuoka Sta from August to November 2021(Yoshimi et al., SSJ, 2022). And we observed the 110 km section between Maibara Sta and Shin-Osaka Sta, with a DAS interrogator at Kyoto Station from August 2022 to February 2023.
On the other hand, We observed an optical fiber cable for 57 km laid in the Yamanashi Prefecture by JR Central from April to May 2022.
In parallel with the DAS observation, we conducted temporary observations using broadband seismometers and accelerometers for comparison of shaking and time calibration.
Fiber-optical cables are installed along the track in a variety of ground and structural conditions such as tunnels, bridges, viaducts, embankments, shelters, and natural ground, and they exhibit characteristic shaking depending on the installation conditions.
In particular, in the tunnels of the Tokaido Shinkansen, the cables are installed on the wall surface and record micro-pressure vibrations when a train passes through. On the other hand, in the tunnels of the Yamanashi Prefecture, the cables are installed on the floor of the central passageway in addition to the wall surface. Comparing the two, the former tends to continue shaking for a long period of time after the train passes, while the latter records the shaking caused by the train passage more accurately. The shaking caused by a Shinkansen train can be up to 100 gal. As a result, the N5226A interrogator manufactured by AP Sensing, which has been used in our observations, saturates in amplitude every time a Shinkansen train passes. This is mainly due to the long gauge length of 5-40 m. Parallel observations with a Neubrex NBX-54000 interrogator with a gauge length of 20 cm showed that both interrogators recorded essentially the same signal, and that the latter observed shaking without saturation.
These observations have detected many earthquakes, ranging from the October 7, 2021 earthquake (M5.9) in the northwestern part of Chiba Prefecture to earthquakes smaller than M1, and can be utilized for various seismological studies.
Yoshimi et al. (SSJ, 2022) confirmed that a matched filter analysis can detect several volcanic low-frequency earthquakes beneath Mt. Fuji that are not in the JMA catalog. It was confirmed that the amplitude of the DAS records changes with the magnitude of the earthquake and the distance from the hypocenter. This information can be used to derive detailed strong-motion prediction equations for each point along the track.
On the other hand, We observed an optical fiber cable for 57 km laid in the Yamanashi Prefecture by JR Central from April to May 2022.
In parallel with the DAS observation, we conducted temporary observations using broadband seismometers and accelerometers for comparison of shaking and time calibration.
Fiber-optical cables are installed along the track in a variety of ground and structural conditions such as tunnels, bridges, viaducts, embankments, shelters, and natural ground, and they exhibit characteristic shaking depending on the installation conditions.
In particular, in the tunnels of the Tokaido Shinkansen, the cables are installed on the wall surface and record micro-pressure vibrations when a train passes through. On the other hand, in the tunnels of the Yamanashi Prefecture, the cables are installed on the floor of the central passageway in addition to the wall surface. Comparing the two, the former tends to continue shaking for a long period of time after the train passes, while the latter records the shaking caused by the train passage more accurately. The shaking caused by a Shinkansen train can be up to 100 gal. As a result, the N5226A interrogator manufactured by AP Sensing, which has been used in our observations, saturates in amplitude every time a Shinkansen train passes. This is mainly due to the long gauge length of 5-40 m. Parallel observations with a Neubrex NBX-54000 interrogator with a gauge length of 20 cm showed that both interrogators recorded essentially the same signal, and that the latter observed shaking without saturation.
These observations have detected many earthquakes, ranging from the October 7, 2021 earthquake (M5.9) in the northwestern part of Chiba Prefecture to earthquakes smaller than M1, and can be utilized for various seismological studies.
Yoshimi et al. (SSJ, 2022) confirmed that a matched filter analysis can detect several volcanic low-frequency earthquakes beneath Mt. Fuji that are not in the JMA catalog. It was confirmed that the amplitude of the DAS records changes with the magnitude of the earthquake and the distance from the hypocenter. This information can be used to derive detailed strong-motion prediction equations for each point along the track.