Name : SHIOBARA,  Hajime
            Position : Associate Professor
            Division/Center : Ocean Hemisphere Research Center
            Research Area : Seismology
 
 

Research :

My research is based on development of ocean bottom seismometers (OBSs) which is aimed to reveal earth interior beneath the
       ocean, where we could not obtain fine structure only from land observations. We make a group for marine seismology and ocean
       bottom solid earth geophysics to perform this aim, because we should work together for marine experiments. My current studies are
       (1) development of a long-term broad-band OBS, (2) fine imaging of mantle beneath the Philippine Sea plate by using these OBSs,
       and (3) OBS surveys for crustal structure, seismic activity and aftershock distribution.

       (1) and (2)
       To understand history of the earth well, it is now believed that we should research the earth from the view of plate and plume
        tectonics, then we need fine image of the whole earth interior. As 70% of the earth surface is covered by the sea, it has been difficult
       to obtain a high resolution structure of the mantle beneath the ocean, such as the western Pacific, only from land data. A long-term
       and broad-band observation is required to detect several large earthquakes used as signal sources, those can penetrate into the deep
       interior.
       The long-term broad-band OBS is designed for the aim above, and it is now on the way to improve the data quality through practical
       observations. By using 15 semi broad-band OBSs, we start a very long profile observation across the Philippine Sea from Dec. 1999,
       which is aimed to make a fine image of the subducting slab of the Pacific plate.

       (3)
       Our group has been developing a Japanese standard OBS for mobile observations such as crustal structure survey and micro seismic
       activity or aftershock study. Observations are performed all over the world with foreign scientists and ships. Currently, I devote to a
       study about a large earthquake occurred south off Ishigaki island (1998/5/4), which located within the Philippine Sea plate. The
       aftershock observation by OBSs made a clear view of the fault plane and its relation with the sea bottom topography.
 

Publications :

S. Ito, R. Hino, S. Matsumoto, H. Shiobara, H. Shimamura, T. Kanazawa, T. Sato, J. Kasahara, and A. Hasegawa, Deep seismic structure of the seismogenic plate boundary in the off-Sanriku region, northeastern Japan, Tectonophysics, 319, 261--274, 2000.

R. Hino, S. Ito, H. Shiobara, H. Shimamura, T. Sato, T. Kanazawa, J. Kasahara and A. Hasegawa, Aftershock distribution of the 1994 Sanriku-oki earthquake (Mw 7.7) revealed by ocean bottom seismographic observation, J. Geophys. Res., 105, 21697--21710, 2000.

M. Mochizuki, B. Brandsdottir, H. Shiobara, G. Gudmundsson, R. Stefansson, and H. Shimamura, Detailed distribution of microearthquakes along the northern Reykjanes Ridge, off SW-Iceland, Geophys. Res. Lett., 27, 1945--1948, 2000.