Grant-in-Aid for Scientific Research (A)
|Allocation Type||Single-year Grants|
|Research Institution||The University of Tokyo|
IWASAKI Takaya Earthquake Research Institute, The University of Tokyo, Professor, 地震研究所, 教授 (70151719)
SATO Hiroshi Earthquake Research Instate, The University of Tokyo, Associate Professor, 地震研究所, 助教授 (00183385)
HIRATA Naoshi Earthquake Research Instate, The University of Tokyo, Professor, 地震研究所, 教授 (90156670)
YOSHII Toshikatsu Earthquake Research Institute, The University of Tokyo, Professor, 地震研究所, 教授 (40012950)
MORIYA Takeo Dep. Geophysics, Hokkaido Univ., Associate Professor, 大学院・理学研究科, 助教授 (60001864)
ARITA Kazunori Dep. Geophysics, Hokkaido Univ., Associate Professor, 大学院・理学研究科, 助教授 (30091408)
|Project Period (FY)
1998 – 1999
Completed(Fiscal Year 1999)
|Budget Amount *help
¥36,600,000 (Direct Cost : ¥36,600,000)
Fiscal Year 1999 : ¥5,300,000 (Direct Cost : ¥5,300,000)
Fiscal Year 1998 : ¥31,300,000 (Direct Cost : ¥31,300,000)
|Keywords||Hidaka / Collision / Hokkaido / Arc / Crust / Deformation / Delamination / Reflection / 島孤地殻|
Our study in 1999 was concentrated in the data processing of seismic reflection data. Our data revealed a clear image of deformation style associated with the arc-arc collision' between the kuril Arc and Northeastern Japan Arc. The obtained reflection section is characterized by
(1) strong westward dipping reflector in range of 3-4 sec in IWT under the eastern flank of the Hidaka Mountains,
(2) eastward dipping reflector at 2 sec in TWT under the. western flank of the Hidaka Mountains.
(3) westward dipping reflector at 4-6 sec in TWT under the middle part of the Hidaka Mountains,
(3) Deep events at 10-1 1 sec in TWT under the eastern edge of the profile.
Data collected on off-line recorders were also completed for the refraction/wide-angle crustal study in the collision zone. A combined analysis of the seismic refection and refraction data indicates the following structural features in the surveyed area.
(1) In the eastern part of the Hidaka Mountains, a material with a velocity of 5.8-6.0 km/s is almost outcr6pped.
(2) The obtained velocity of 5.8-6.0 km/s is rather small as those of the middle crustal or lower crustal rocks which are expected to expose in the Hidaka Mountains. This suggests that the obducted crustal rocks are highly deformed and merged into the surrounding low-velocity upper crustal material.
The seismic image obtained forms a part of the delamination-wedge structure associated with the arc-arc collision. The reflectors in the eastern part of the Hidaka Mountaines Is a upper part of the reflective lower crust of the Kuril Arc overriding westward. Our results provide important key for understanding collision process occurring in this region.