|Monogr. Environ. Earth Planets, Vol. 2 (No. 2), pp. 23-63, 2014||doi:10.5047/meep.2014.00202.0023 ISSN: 2186-4853|
International Research Institute of Disaster Science, Tohoku University, Sendai 980-8579, Japan
(Received March 3, 2013; Revised January 15, 2014; Accepted January 16, 2014; Online published March 31, 2014)
Citation: Fujimoto, H. (2014), Seafloor geodetic approaches to subduction thrust earthquakes, Monogr. Environ. Earth Planets, 2, 23-63, doi:10.5047/meep.2014.00202.0023.
Abstract: Observation systems and some observed results of seafloor geodesy are reviewed with a focus on the research activities of Japanese groups, especially those of Tohoku University. Seafloor acoustic ranging has been adopted as the simplest way to continuously monitor local crustal activities. The GPS-Acoustic (GPSA) method has been the most important for seafloor positioning. It seems that commercial technologies can be used to lessen the considerable differences in repeatability and spatio-temporal resolution of GPSA and land based GPS. Ocean bottom pressure sensors have been used to continuously monitor vertical crustal movements. Improvements in the resolution and long-term stability of pressure sensors will lead to monitoring slow slip events and interplate locking. Ocean bottom and underwater gravimeters have been developed for precise gravity mapping and monitoring mass change beneath the seafloor. The 2011 Tohoku-oki earthquake is an historical event demonstrating that seafloor geodetic observations are crucial to understanding the mechanism of giant earthquakes. Coseismic displacements detected through geodetic observations on the seafloor have indicated huge slips on the shallow part of the plate boundary. A slow slip event near the zone of the coseismic slip preceding the main event has been detected from slight pressure variations. This illustrates the importance of real-time monitoring with a cabled seafloor observatory, which is also a key to establishing a reliable early tsunami warning system.
Keywords: Seafloor geodesy, Seafloor crustal movement, 2011 Tohoku-oki earthquake, Interplate coupling, GPS-Acoustic, Ocean bottom pressure.
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