In recent years, dynamic nature of the Earth's interior is recognized as a result of various interactions. It is necessary to have an observation network of global scale in order to totally understand the physical phenomena on and within the Earth. From this view-point, ocean, which covers about 70% of the Earth's surface, can be regarded as a window to look into the Earth's interior without disturbance by complicated geological noises of the continental crust. At the same time, ocean, especially the Pacific prevents us from building geophysical observation stations. In "Ocean Hemisphere Network Project (OHP)" largest efforts have been paid to deploy a well-spread geophysical network (the OHP network) in the Pacific to investigate the structure and dynamics of the mantle and the core and to reveal the physics of the Earth's activity. Installation of the OHP network was completed in 2001.

The Ocean Hemisphere Research Center (OHRC) is the newest component of Earthquake Research Institute since 1997. The OHRC has three tasks: Long term operation of the OHP network (cooperatively with JAMSTEC), data distribution and exchange (also cooperatively with JAMSTEC), and development of new instruments and sensors. Besides these tasks, the activity of the OHRC are focused on the study of the stagnant slab in the western Pacific subduction zone, by long term deployment of newly developed instruments such as Ocean Bottom Seismometers (OBS) and Ocean Bottom Electromagnetometers (OBEM). Scientists in the OHRC are also enthusiastic in working at the frontier of geophysical research to understand geophysical phenomena by regarding the Earth as a composite of solid and fluid materials.