58. 世界の特殊な地震地区の活動について : 其の6 コロンビア,ルーマニアおよび南サンドウィッチ諸島

• Main Authors: Santo, Tetsuo, 129889
• Language: English
• Published: 東京大学地震研究所 1971
• Subjects: 453; Sandwich Islands; South Sandwich Islands
• Online Access: https://repository.dl.itc.u-tokyo.ac.jp/record/33270/files/ji0486005.pdf

application/pdf Focal distribution of upper mantle earthquake nests in three seismic areas-in the northern part of Colombia, around the Carpathian, bend in Rumania and in the northern part of the South Sandwich Islands arc-were studied with relation to the topographies around the areas. An inclined focal zone existing only in the upper mantle beneath the Oriental Mountain chain in Colombia was suggested to be a remnant of the lithosphere which underthrusted in the previous epoch. Upper mantle earthquakes originating beneath the Carpathian bend distribute vertically along the NW-SE profile perpendicular to the axis of the Carpathian bend. This situation resembles that beneath the Hindu Kush. There are, however, almost no events in the crust above the upper mantle earthquake nest. Foci distributions in the South Sandwich Islands region along the profiles perpendicular to the trend of the trench look like having characters different from those in other Island arc-trench regions. That is, the foci plane cannot be well recognized and foci do not penetrate so deep as is expected from the well developed trench. The occurrence of upper mantle earthquakes in the northernmost terminal of the South Sandwich Islands arc is a quite peculiar one. Foci are gathering into a U shaped space beneath the area of about 1.3°×0.7° centering at 27.3°W, 56.1°S. Such focal distribution cannot be explained from plate tectonics associated with the Island arc-trench system.|現在のプレート・テクトニクスでは説明がむづかしい場所と震源分布をもつマントル地震活動地区が世界中には特に大陸内部に存在する.たとえば,ヒンズー・クシや北ビルマのそれらもその代表的な例であった.本篇で取扱った三つの地区のマントル地震も,まさにその例といえる. departmental bulletin paper