フォッサマグナの基盤構造と現在の地殼運動

概要

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100 years have past since Edmund NAUMANN discovered the Fossa Magna in 1876. He thought it as a kind of large rift dividing the Japanese arc into the northeastern and southwestern limbs. He regarded the islands as a single Palaeozoic folded zone and afterwards transversed by the rift accompanied by volcanic zones. On the other hand Edward SUESS and Toyokichi HARADA considered the islands in terms of two tectonic units, the northern Sachalin System and the southern Chinese System, joined in the manner of syntazis in the Fossa Magna. Since the argument of NAUMANN vs. HARADA concerning the tectonic units of Japanese islands, hot discussions have continued concerning the tectonic signifficance of the Fossa Magna.<BR>After structural analyses of the folded zones in the Akaishi Mts., the senior author has confirmed the Fossa Magna as a large meridional left lateral fault, holding 100 kms of displacement. It is accompanied by a large and wide drag zone in the western side, consisting of minute and numerous faults and cracks. Owing to the fragmentation of the drag zone, there has been no large earthquake in these areas. In order to confirm very slow crustal movements and regional strains of the fault zone, we measure precise distances among several radial and triangular nets in the zone by means of an electro optical instrument “Geodimeter 700”. Results of surveys are also summerized in this paper.
社団法人東京地学協会の論文