JDR Vol.18 No.7 pp. 730-739
doi: 10.20965/jdr.2023.p0730


Analysis of Orientation Changes of S-Net Accelerometers due to Earthquake Motions

Yadab P. Dhakal ORCID Icon and Takashi Kunugi ORCID Icon

National Research Institute for Earth Science and Disaster Resilience (NIED)
3-1 Tennodai, Tsukuba, Ibaraki 305-0032, Japan

Corresponding author

April 20, 2023
August 16, 2023
October 1, 2023
S-net, ocean-bottom seismographs, strong motions, rotation of sensors, earthquake early warning

S-net is a large-scale seafloor observation network for earthquakes and tsunamis around the Japan Trench, consisting of 150 observatories equipped with seismometers and pressure gauges. The sensors have been set up inside cylindrical pressure vessels, which have been buried in the shallow-water regions (water depth <1,500 m), while the vessels have been laid freely on the seafloor in the deeper-water regions. Previous studies showed that the cylindrical pressure vessels rotate during strong shakings due to poor coupling with the seabed sediments, thus making it difficult to retrieve the actual ground motions. We investigated the static changes in the orientations of S-net accelerometers due to shakings from 1,878 earthquakes of Mj greater than 4 that occurred around the network, and found that rotations as large values as 16° were observed during the 2022, Mj 7.4, off-Fukushima Prefecture earthquake. We estimated the threshold acceleration levels after which the sensors are likely to rotate at all S-net stations separately and found that the threshold values lie mostly between 5 and 50 cm/s2. Finally, we discussed the observed peak accelerations and velocities at the S-net stations with those recorded on land, where high-quality records were obtained, during the 2022, Mj 7.4 earthquake, which was also the largest magnitude earthquake to occur in the region after the network commenced operation. The results presented herein complement several previous studies and form the basis for more comprehensive future investigations.

Cite this article as:
Y. Dhakal and T. Kunugi, “Analysis of Orientation Changes of S-Net Accelerometers due to Earthquake Motions,” J. Disaster Res., Vol.18 No.7, pp. 730-739, 2023.
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Last updated on Nov. 24, 2023