Joint sea-land seismological observation at peculiar mid-oceanic ridges.

大西洋中部山脊是板块诞生的地方。亚速尔群岛位于三大板块交界处，欧亚板块、北美板块和非洲板块同时诞生。此外，亚速尔群岛-直布罗陀断裂带(AGFZ)从亚速尔群岛三重结点(AZT)向东延伸至直布罗陀海峡。1755年欧洲历史上最大的地震里斯本地震就发生在这一断裂带上，但迄今为止，AZT和AGFZ的地震活动和地下结构都没有得到很好的研究，因为所有的地震学观测都是在相距数千公里的大西洋两岸进行的，这限制了详细的研究。我们认为，我们的海底地震仪(OBSS)是解决这些问题的有力工具。我们的OBS体积小、可靠性高、灵敏度高。数十个OBS的部署使得能够展示非常详细的地震活动以及三维SEI…在一九九二年和一九九三年，我们先后向大西洋引进了约30个开放式保税仓。1992年，我们对AZT地区的地震活动进行了密集的阵列测量，1993年，我们再次在AGFZ地区进行了类似的大规模实验。我们的OBSS在两次探险中都捕捉到了1000多次微震。除了亚速尔群岛地区，我们还进行了密集的OBS研究，其中我们使用了30个OBS，以说明挪威近海非常详细的地壳结构，在那里，被认为是5500万年前开始的大西洋的残余起源保持在流动玄武岩之下。对于海上常用的地震反射方法来说，流动玄武岩是很难穿透的岩石，而我们的OBS折射测量可以穿透到地层以下。在1992年的实验中，我们在亚速尔群岛部署了29个OBS，覆盖了250×150公里的区域。我们在后勤方面得到了里斯本大学和葡萄牙海岸警卫队的宝贵帮助。巴黎大学在一些岛屿上部署了7台无线电波遥测地震仪进行这项研究，结果发现微震只发生在连接亚速尔群岛的狭窄构造带上，其他地方没有地震活动。地震震中呈梯形，与构造带呈顺时针方向。我们的结果表明，相当小的微板表现为书架上的书籍，这是对三重结构造的发现。1993年，我们在AGFZ附近部署了25个OBSS。实验分为两部分：微震调查和利用气枪进行折射研究。OBS捕捉到了许多地震，折射研究取得了成功。由于获得的数据很多，分析仍在进行中，但我们对获得该地区构造的各种发现持乐观态度。较少

Mid-Atlantic Ridge is the place where plate is being born. Azores Islands are situated immediately on the triple junction where three plates, Eurasian plate, North American Plate and African Plate, are simultaneously born. Also, the Azores-Gibraltar Fracture Zone(AGFZ) extends from Azores Triple Junction (AZT) to the east until Gibraltar strait. The largest European earthquake in the history, Lisbon earthquake, 1755, took place on this fracture zone.However, both seismic activity and underground structure for AZT and AGFZ have not been well investigated since all the seismological observations had been so far made from thousands of km apart, i.e. from both sides of Atlantic Ocean, which consequently restricted the detailed studies.We believe that our Ocean Bottom Seismographs (OBSs) are powerful tool to solve these problems. Our OBS is small, reliable and highly sensitive. Deployments of tens of OBSs enable to illustrate a very detailed seismic activity as well as three dimensional sei … More smic structures.We brought about 30 OBSs to the Atlantic in 1992 and in 1993. In 1992 we made a dense array measurements of seismic activity in the AZT area, and in 1993 we made again the similarly extensive experiments in the AGFZ area. More than 1000 micro earthquakes were caught by our OBSs for both expeditions. Apart from the Azores area, we also made a dense OBS studies, in which we used 30 OBSs, to illustrate a very detailed crustal structure off Norway, where a remnant initiation of the Atlantic Ocean, which has been believed to initiate 55 million years ago, is kept beneath the flow basalt. The flow basalt is very impenetrable rock for the usual seismic reflection method used in the sea, however our OBS refraction survey can penetrate beneath the layer.In the 1992 experiment, we deployed 29 OBSs along Azores Islands, which covered 250 x 150km area. We obtained a valuable help from Lisbon University and Portuguese Coast Guard for logistics. University of Paris deployed seven radio-wave telemetry seismographs for this study on some islands.As a result, we found that microearthquakes occurred only along a narrow tectonic belt which connect Azores Islands, and no seismicity elsewhere. The earthquake epicenters are in a form of an echelon, which is clockwise to the tectonic belt. Our result suggests that microplates with rather small size behaves as books on the bookshelf, which is a discovery for the tectonics of the triple junction.In 1993 we deployed 25 OBSs in the vicinity of AGFZ. The experiment was two-fold : microearthquake survey and refraction study by the use of air-guns. Lots of earthquakes were caught by the OBS, and the refraction study was successful. Because the obtained data were vast, the analysis is still being done, however we are optimistic to obtain various findings for the tectonics of the region. Less