Crack-Anticrack Interaction in Faulting

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; R o o t E n t r y F $ C o m p O b j b W o r d D o c u m e n t O b j e c t P o o l $ $ 4 @ ( ) * + , - . / 0 1 2 F Microsoft Word 6.0 Document MSWordDoc Word.Document.6 ; si 9526983 Fletcher Determination and qualification of the micromechanics of faulting is an important problem, both in addressing events prior to and during earthquakes, and in interpreting observations from experiments and from the field. The role of mode I opening cracks has always been a basic element in the formulation of the micromechanics of faulting. Recently, a model for the organization of the fault of fault zone resulting in a deep focus earthquake has been based upon the interaction and propagation of mode I closing anticracks (Green and Burnley, 1989; Green, 1994, 1995), the anticracks being thin laminae of the higher-density spinel formed in the olivine- spinel phase transformation. Fault zones which arise from the organized interaction of cracks and anticracks are observed in the deformed limestones of the central Appalachians, and analogous structures have been reported from other settings. In these occurrences, the cracks are represented by veins, and the anticracks by solution seams. In view of the role of pressure solution, the process of formation of these structures is slow, but the weakened zone might eventually fail by rapid, seismic faulting. These structures are also significant in their own tectonic setting, besides illustrating a process of potentially broader scope. The aim of the proposed research is to study these structures through detailed observation, at field mapping to thin-section scale, and to develop mechanical models for their initiation and evolution, at micromechanical and macroscopic levels. ; Oh +' 0 S u m m a r y I n f o r m a t i o n ( ' $ H l D h R:\WWUSER\TEMPLATE\NORMAL.DOT 9526983 Felicia Smith Felicia Smith @ @ @ @ Microsoft Word 6.0 1 ; e = e j j j j j j j Q 1 3 T 5 Q j Q j j j j ~ j j j j 9526983 Fletcher Determination and qualification of the micromechanics of faulting is an important problem, both in addressing events prior to and during earthquakes, and in interpreting observations from experiments and from the field. The role of mode I opening cracks has always been a basic element in the formulation of the micromechanics of faulting. Recently, a model for the organization of the fault of fault zone resulting in a deep focus earthquake has been based upon the interaction and propagation of mode I closing anticracks (Green and Burnley, 1989; Green, 1994, 1995), the anticracks being thin laminae of the higher-density spinel formed in the olivine- spinel phase transformation. Fault zones which arise from the organized interaction of cracks and anticracks are observed in the deformed limestones of the central Appalachians, and analogous structures have been reported from other settings. In these occurrences, the cracks are represented by veins, and the anticracks by solution seams. In view of the role of pressure solution, the process of formatio