Evolution and deformation process of the Hidaka Collision Zone, Central Hokkaido, Japan.

1999年我们的研究主要集中在地震反射资料的数据处理方面。我们的数据揭示了与千岛岛弧和日本东北岛弧之间的弧-弧碰撞有关的变形样式的清晰图像。所获得的反射剖面的特征是：（1）在日高山东侧的行波管上，在3-4秒范围内，有强的向西倾斜的反射层;（2）在日高山东侧的行波管上，在2秒范围内，有向东倾斜的反射层。日高山脉的西翼。(3)在日高山脉中部的行波管中，在4-6秒处有向西倾斜的反射层;（3）在剖面东缘的行波管中，在10- 11秒处有深部地震。地震反射和折射波资料的综合分析表明，测区具有以下构造特征：(1)在日高山东部，一种速度为5.8-6.0 km/s的物质几乎被挤出。(2)所得的速度为5.8-6.0 km/s，与预计在日高山出露的中地壳或下地壳岩石的速度相当小。这表明仰冲地壳岩石发生了强烈的变形并与周围低速的上地壳物质融合，所获得的地震图像构成了与弧-弧碰撞有关的拆离-楔状构造的一部分。日高山东部的反射体是向西隆起的千岛弧反射下地壳的上部。我们的研究结果为理解该区域的碰撞过程提供了重要的线索。

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,and(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.