This area
is near an active fault that moved at the time of the Great Kanto Earthquake
in 1923. Sagami Bay is where the North American Plate, which carries the
eastern Japan, and the Philippine Sea Plate collides with, and has experienced
countless earthquakes since ancient times. With the movements of the plate
and the activity of the magma beneath it, cold water containing chemical
substances seeps out from the active fault, and this is where bacteria that
obtain their nutrition from the chemical substances and the giant white
clams coexist. It had been extremely difficult to find the exact location
of the active fault, but here the clams were clearly pointing it out. Long-term
observation such as this allows us to understand the movement of plates
and magma activity, which are the cause of earthquakes. In 1993 JAMSTEC
established the Real-Time Deep Sea Floor Observatory off Hatsushima island
at a depth of 1,174 meters in the area of the giant white clams. Linked
to the land station by optical fiber cable, the observatory monitors the
state of the organism populations, ground and water temperature, the occurrence
of swarm earthquakes, and water turbidity in real time.
Many massive earthquakes occur on the ocean floor at the boundaries between
plates, and continuous monitoring at the ocean floor is essential to gain
a detailed understanding of earthquake activities and submarine tectonics.
JAMSTEC established long-term deep seafloor observatories off Cape Muroto,
Kochi Prefecture, where the Philippine Sea Plate is subducting, and off
Kushiro-Tokachi, Hokkaido, where the Pacific Plate is subducting.
By establishing these long-term observation systems on the ocean floor,
JAMSTEC is able to observe crustal movements and minor earthquakes that
cannot be detected from land, and is using these data to estimate plate
deformation and subsurface magma activities.
JAMSTEC's future plans are to expand the long-term observation network for
submarine earthquakes to plate boundaries in the Pacific Ocean, the Sea
of Japan and toward the Nansei Islands.
Expanding this network to distant sea areas is extremely costly, so JAMSTEC
is also working with other Japanese research institutions to connect various
measuring instruments to existing submarine communication cables that are
no longer in service in an effort to carry out real-time observation.
At some stage in the future, there may come a day when an international
cooperative effort will realize an earthquake observation network that envelopes
the entire Pacific Plate. |
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