SAFODコアからの深層サンアンドレアス断層の低強度
David A Lockner1, Carolyn Morrow, Diane Moore
1US Geological Survey, Menlo Park, California 94025, USA. dlockner@usgs.gov
Nature
|March 29, 2011
まとめ
サンアンドレアス断層は,サポニット粘土による深さでは驚くほど弱い. この発見は,断層の這い回る動きを説明し,流体圧に関する以前の理論に異議を唱えた.
科学分野:
- 地質学 地質学 地質学
- テクトニクス (地質学) とは
- ミネラロジーは,鉱物学です.
背景:
- サンアンドレアス断層は,太平洋プレートと北米プレートとの間に重要な右横の動きを示しています.
- 断層の特徴は,はっきりとロックされた部分とクレイピングの部分で,ロックされた部分では大きな地震が発生します.
研究 の 目的:
- サンアンドレアス断層の中核の機械的性質を深部で調査するために.
- 断層の爬行地帯における変形を制御する要因を決定する.
主な方法:
- サンアンドレアス断層深層観測所 (SAFOD) から得られた断層コアサンプルの実験室での強度測定.
- 垂直2.7kmの深さでの鉱物組成とin situ条件の分析.
主要な成果:
- SAFODの場所にあるサンアンドレアス断層は,摩擦係数 (0.15) が低く,極めて弱い.
- この弱さは,弱いスメクチート粘土鉱物であるサポナイトの存在に起因する.
- サポナイトは壁岩とサーペンチナイトの反応から形成され,鉱物によって制御される弱体化メカニズムを示しています.
結論:
- サンアンドレアス断層の爬行部分の変形は,サポナイトのような弱い鉱物の存在によって制御されます.
- これは,故障の弱さの主要な原因として高圧流体を示唆する以前の仮説と対照的です.
- この研究は,断層のストレス状態の自己一貫したモデルを提供し,SAFODサイトにおける固有の弱点を強調しています.
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