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

1987年，我们利用我们研制的海底地震仪（OBS）对挪威最长的峡湾--松恩峡湾（Sognefjord）（长200公里）的地壳结构进行了详细的研究，并于1988年对挪威海岸与莫恩斯海岭之间的东北大西洋海底进行了非常详细的三维结构研究。1989年，我们还对挪威近海的天然地震活动进行了详细的研究。在可控震源试验中，我们利用挪威和西德德国的考察船在海底布设了20 - 25个OBS。在1987年的实验中，我们获得了松恩峡湾下的详细结构，在那里我们发现了与地表地质结构的良好对应关系，并追踪了边界的更深延伸。在1988年的实验中，进行了两次连续的实验，每次使用20 - 25个OBS，这两项试验都是迄今为止进行的最高密度试验。罗弗敦附近地区被流动熔岩覆盖，无法通过多通道反射研究穿透，因此只有OBS可以研究该层下的地壳结构。这一结果有助于研究大西洋的开放。在1989年的实验中，第一次在挪威海岸和莫恩斯海岭之间的一个地区研究了非常小的地震的详细地震活动。从陆地上的观测中无法观察到这种活动。这一研究成果对该地区板内地震的研究具有一定的参考价值。

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.