北米東部の下部で撮影された,鋭い石層-アステノスフィアの境界線
Catherine A Rychert1, Karen M Fischer, Stéphane Rondenay
1Department of Geological Sciences, Brown University, Box 1846, Providence, Rhode Island 02912, USA. Catherine_Rychert@Brown.edu
Nature
|July 29, 2005
まとめ
リトスフィア-アステノスフィアの境界は予想以上に鋭いので,温度だけでなく,部分的な融解または揮発性物質がアステノスフィアを弱体化させることを示唆しています. この地震画像は,地球のマントルの動力学に関する重要な洞察を明らかにしています.
科学分野:
- 地質物理学 地質物理学とは地質物理学です.
- 地震学 地震学とは
- テクトニクス (地質学) とは
背景:
- プレート構造は,石層圏がアステノスフィア上空を移動することで成り立っている.
- リトスフィアとアステノスフィアの境界の性質は,機械的な強さの違いを理解するために重要である.
- この境界における地震速度のグラデーションは,物理的,化学的性質についての洞察を提供します.
研究 の 目的:
- 地震データを用いて,石層-アステノスフィアの境界の鋭さを調査する.
- 境界の特徴に起因する物理的,化学的性質を制限する.
- 熱的および組成的/溶融による弱体化メカニズムを区別する.
主な方法:
- 北米東部の変換された地震相の分析.
- リトスフィアの底辺の地震速度のグラデーションをイメージする.
- 特定の深さの範囲におけるシーア波の速度低下を定量化する.
主要な成果:
- リトスフィア-アステノスフィアの境界 (90-110 kmの深さ) で,急激な地震速度のグラデーションが観測されました.
- シャー波の速度は11km以下で3~11%低下した.
- この鋭い境界線は,純粋な熱グラデントと矛盾しています.
結論:
- アステノスフィアは,おそらく,いくつかのパーセントの部分的な溶融を含んでいるか,または揮発性物質で濃縮されている.
- 温度だけでなく,これらの要因が,アステノスフィアの弱さを説明する.
- この発見は,マントルの流れとプレート構造のモデルを洗練している.
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