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Japanese Agency Observes Tsunami with Submarine Optical Cable

Japanese Agency Observes Tsunami with Submarine Optical Cable

   Tokyo, June 6 (Jiji Press)--The Japan Agency for Marine-Earth Science and Technology, or JAMSTEC, said Thursday that it observed a tsunami that occurred off Torishima, an island in the Izu chain in the Pacific, in October last year using the long-distance fiber-optic cable it placed for research purposes on the seabed off Cape Muroto in the western prefecture of Kochi.
   A tsunami changes water pressure in the sea and the submarine topography, slightly altering the shape of the fiber-optic cable. This creates a gap in the round-trip time of a laser light transmitted through the cable from a base station on the ground, making it possible to observe tsunami and earthquakes.
   The cable extends some 100 kilometers southward from an area near Cape Muroto and can identify a section of several to several tens of meters whose shape changed due to an earthquake or tsunami.
   It successfully observed a tsunami between a point some 60 kilometers off the cape and an area near the cape as it continued a survey on slow earthquakes that had occurred along the Nankai Trough since January 2022.
   Currently, the fiber-optic cable cannot estimate the height of a tsunami. However, Takashi Tonegawa, a senior researcher at JAMSTEC, said, "If we understand the physical characteristics of the optical fiber and subseafloor structure in advance, the height of a tsunami can be calculated."

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