海底地震計を用いた九州西方沖・沖縄トラフにおける地殻・上部マントルの地震波速度構造調査

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タイトル別名
  • Research Report of the Crust and Upper Mantle Structure in the Okinawa Trough, off West Kyushu by Using Ocean Bottom Seismometer
  • カイテイ ジシンケイ オ モチイタ キュウシュウ セイホウオキ オキナワ トラフ ニ オケル チカク ジョウブ マントル ノ ジシンハ ソクド コウゾウ チョウサ

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抄録

The Okinawa Trough is located in the・ back-arc region of the Ryukyu Island arc, and is considered to be an active spreading area. In fall of 1999, seismic survey using ocean bottom seismometers was conducted to obtain the detailed seismic structure in the northernmost part of the Okinawa Trough. The total crust thickness is 25 km including a sedimentary layer. The velocity of the upper crust changes from 5.7-6.0 km/s in the upper part to 6.1-6.2 km/s in the lower part. And its thickness changes from 3 km to 9 km. The lower crust of which velocity slightly changes from 6.5-6.7 km/sin the upper part to 6.8-6.9 km/sin the lower part has uniform thickness of about 15 km. The Pn velocity is determined to be 7.7-7.8 km/s. The seismic structure suggests that the northernmost part of the Okinawa Trough is in the incipient stage of a backarc rifting.

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