Name : IWASAKI,  Takaya
            Position : Professor
            Division/Center : Earthquake Information Center
            Research Area : Controlled Seismology
 

RESEARCH

Japanese Islands belong to the subduction zones developed along the western rim of the Pacific Ocean. The crustal and upper mantle structures of the Japanese Islands provide important information in understanding tectonics and dynamics of the subduction system. Our laboratory has conducted seismic refraction/wide-angle reflection experiments under the cooperation with scientists from other Japanese universities to elucidate not only velocity structure but also the mineral compositions and petrological features of the crust, which are essentially important in establishing crustal evolution process of the surveyed area.

Now, we are performing the above studies in a more sophisticated manner, in which the island arc crust is investigated by multi-disciplinary project including seismic refraction profiling, seismic reflection profiling and microearthquake observation. The seismic refraction method provides us large-scale crustal heterogeneity, while the reflection method reveals small-scale inhomogeneity within the crust such as active fault systems. The microearthquake observation is quite important to investigate the relation between the seismic activity and crustal heterogeneity, which provide an important key to understand the mechanism of earthquake occurrence within the subduction region.

An intensive expedition in 1997-1998 in northern Honshu arc is the first example of such a multi-disciplinary project. A 500-kn long onshore-offshore wide-angle line revealed large-scale structural variation from the Japan Trench to the Sea of Japan. In the land area, we elucidated deformation style of the crust associated with the opening of the Sea of Japan.
 

PUBLICATIONS

Ozel, O., Iwasaki, T., Moriya, T., Sakai, S., Maeda, T., Piao, C., Yoshii, T., Tsukada, S., Ito, A., Suzuki, M., Yamazaki, T. and Miyamachi, H., Crustal structure of central Japan and its petrological implications, Geophys. J. Int., 138, 257--274, 1999.

 Iwasaki, T., Yoshii, T., Hirata, N. and Sato, H., New features of island arc crust inferred from seismic expeditions with controlled sources in Japan, International Workshop on Seismotectonics at the Subduction Zone -Toward the breakthrough in the next century-, Tsukuba, Japan, 29 Nov.-1 Dec., 1999, 55--72, 2000.

Sato, H., Hirata, N., Ikeda, Y. and Iwasaki, T., Geometry of active reverse faults in Northern Japan, International Workshop on Seismotectonics at the Subduction Zone -Toward the breakthrough in the next century-, Tsukuba, Japan, 29 Nov.-1 Dec., 1999, 209--215, 2000.