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IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS016 Poster presentation 2356
Repeated Observation of Seafloor Crustal Deformation Using a
GPS/Acoustic System
Prof. Keiichi Tadokoro
Research Center of seismology and Volcanology Nagoya University IASPEI
Masataka Ando, Shingo Sugimoto, Takashi Okuda, Ryoya Ikuta, Tsuyoshi
Watanabe, Keizo Sayanagi, Masahiro Kuno, Jin Yasuda, Daisuke Muto
The Nankai Trough is one of the active plate boundaries where the major subduction earthquakes,
Nankai and Tonankai earthquakes, repeatedly occur. The source regions of the earthquakes are located
beneath the sea bottom, and it is necessary to monitor the crustal activities, such as seismicity and
crustal deformation, for the sake of earthquake prediction and disaster prevention. One of the useful
tools to monitor seafloor crustal deformation is the observation system composed of the acoustic
ranging and kinematic GPS positioning techniques. We install seafloor benchmark composed of three
sea bottom transponders for acoustic ranging. We have installed the seafloor benchmarks at three sites
close to the mid-Nankai Trough. We repeatedly observed at the two sites among them ten times at
each benchmark from 2004. The result of the repeated observation shows that the repeatability of the
measurement is about +/-3 cm for each horizontal component. The coseismic crustal deformation due
to M7 class earthquakes was also detected at the sea bottom benchmark. We installed four benchmarks
also at the Suruga Trough which is located at the northern margin of the Nankai Trough. We measured
the benchmark 14 times for about a year. We observed a displacement vector of (-3.8+/-3.3, 0.5+/-
2.1), which is consistent with plate convergence at the region considering the error values.
Keywords: seafloor crustal deformation, nankai trough, acoustic ranging