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Integrated Earthquake Observation and Research Group

Integrated Earthquake Observation and Research Group

写真 Integrated Earthquake Observation and Research Group
Group Leader
Yasushi ISHIHARA

  • Research on subseafloor tectonic activities, structure and phenomena using seismological techniques
  • Research on geophysical observation aiming interaction with solid earth, marine and atmosphere
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Integrated Earthquake Observation and Research Group

Although real-time earthquake observations using cables connecting seismographs installed on the seafloor, such as DONET, has started, they are still limited in number, and usually ocean-bottom seismographs housed in water and pressure-tight containers are used for earthquake observation on the seafloor. Ocean-bottom seismographs are thrown from a vessel to the seafloor of the research area, surfaced after a certain period of observation by cutting off the weight, and the observation data is collected (called as ocean bottom mobile observation). By deploying an ocean-bottom seismograph network mainly in seismogenic zones in sea areas around Japan and observing natural earthquakes, the Integrated Earthquake Observation and Research Group promotes research, including clarification of the actual conditions of seismic activity below the seafloor that are difficult to determine only by observation from land, and research to clarify the relationship between the seismicity pattern and subseafloor structure. We also aim to research the deep parts of the trench, which is the center area of seismogenic zone, by making full use of the ultra-deep ocean bottom seismographs which may be used for the observation on the deep seafloor below a depth of 6,000 m, and to compare the seismic activity and structure with those in other trench areas. Moreover, in data analysis, we promote development of advanced data processing techniques, such as investigating the subseafloor structure making use of information that is usually treated as noise, and thus work on understanding subseafloor conditions and plate activities from a new point of view. In addition, the group helps deploy a geophysical observation network, including seismic observation, that is developed within an international framework and intended for Southeast Asia and ocean islands in the West Pacifi c area. It supports fundamental observations in the region for seismology, and is also utilized for monitoring largescale disasters caused by earthquakes and tsunamis, and analysis of atmospheric and oceanic phenomena.


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Drawing showing seismic activity around the Japan Trench off Miyagi Prefecture acquired with ultra-deep ocean bottom seismographs. The circles in the figure.
above represent the location of seismic centers, and colors represent their depth. The white rhombuses represent the location of seismographs. The figure below represents a view where hypocenters are projected on a cross section of seismic structure by reflection survey.
figure
Ocean-bottom seismograph used for short-term mobile observation