The mechanisms summarized are as follows 1 ) compressional normal stress ; 2 ) ductile and / or viscous deformation in bedding fault since incompetent bed is susceptible to plastic flow ; 3 ) higher likelihood of clay / shale smearing ; 4 ) foliation fabric whose sealing capacity is enhanced greatly in direction perpendicular to foliation 其机理可归纳为四个方面： 1 )压性的正应力； 2 )以韧性及粘性变形为主，因为非能干岩层易塑性流变； 3 )涂抹效应强； 4 )面理化组构，垂直面理方向的封闭能力大大增强。
