RESEARCH OF DETAILED STRUCTURE BENEATH ICELANDIC PLATEAU BY USE OF OCEAN BOTTOM SEISMOGRAPHS, WITH A COOPERATION BETWEEN JAPAN AND NORWAY

利用我所研制的海底地震仪(OBS)，我们于1987年对挪威最长的峡湾Sognefjord(全长200公里)进行了详细的地壳结构研究，并于1988年对挪威海岸至莫恩斯海脊之间的东北大西洋海底进行了非常详细的三维结构研究。此外，我们还对1989年挪威近海的自然地震活动进行了详细的研究。在可控震源实验中，诺威和西德的科考船在海底部署了20-25个OBS。在1987年的实验中，我们获得了Sognefjord下的详细结构，在那里我们发现了与地表地质结构很好的对应关系，并追踪到了更深层次的边界延伸。在1988年的实验中，我们连续进行了两次实验，每一次都使用了20-25个OBS，都是迄今为止密度最高的实验。罗福滕附近地区被流动的熔岩覆盖，而多通道反射研究不可能穿透这一流动熔岩，因此只有OBS才能研究地层下的地壳结构。这一结果有助于研究大西洋的开阔。在的实验中，首次在挪威海岸和莫恩斯海脊之间的地区研究了非常小地震的详细地震活动。从陆地上的观测看不到这一活动。这项研究有助于研究该地区以前不太为人所知的板内地震。

By using ocean bottom seismograph (OBS) which were developed in our institutes, We made researches of detailed crustal structures of Sognefjord, which is the longest fjord in Norway with a length of 200 km) in 1987, and a very detailed three dimensional structure beneath northeast Atlantic Ocean bottom between Norwegian coast and Mohns Ridge in 1988. Also, we made a detailed study of natural earthquake activities off Norway in 1989.In the controlled source experiments, 20 - 25 OBS were deployed on ocean bottom by research ships of Noway and West Germany. A powerful airgun array was used for the controlled source.In the 1987 experiment, we obtained a detailed structure beneath Sognefjord where we find a good correspondence with a surface geological structure and traced a deeper extension of the boundary.In the 1988 experiment, two successive experiments were carried out, each of which made use of 20 - 25 OBS, Both were the highest density experiment which were made to date. The region off Lofoten is covered by a flow lava which is impossible to penetrate by multichannel reflection study so that only OBS could study the crustal structure beneath the layer. The result has helped to study the opening of the Atlantic Ocean. In the 1989 experiment, detailed seismic activity with very small earthquakes has been studied for the first time in a region between Norwegian coast and Mohns Ridge. The activity had not been able to be observed from the observations on land. The research has helped the study of the intraplate earthquake in the region which had not been well known.