--> --> Abstract: Fault Zone Weakening in Low-Angle Normal Faults</span>
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Previous HitFaultNext Hit Zone Weakening in Low-Angle Normal Faults

Steven A.F. Smith

Department of Earth Sciences, University of Durham, United Kingdom, DH1 3LE

[email protected]

Traditional ‘Anderson-Byerlee’ frictional Previous HitfaultNext Hit models predict that normal faults should initiate at dips of ~60°, rotate and lock up due to friction at angles of ~30-40°. This prediction seems inconsistent with the increasingly wide documentation of active Low-Angle Normal Faults from around the world. Recent models explain continued slip on LANF over long periods of time by invoking syntectonic changes in Previous HitfaultNext Hit rock rheology causing ‘Previous HitfaultNext Hit zone weakening’. This project will adopt a multidisciplinary approach to increasing our understanding of several important factors in the evolution of LANF, including Previous HitfaultNext Hit zone geochemistry, fluid flow and alteration histories, and the controls on Previous HitfaultNext Hit zone architecture.

The Zuccale LANF is very well exposed on the Island of Elba, western Italy. Significantly, recent investigations in central Italy have highlighted the existence of an active LANF – the Altotiberina Previous HitFaultNext Hit - which produces abundant microseismicity. Field observations of the exhumed Zuccale LANF can therefore be used to gain key insights into processes currently occurring at depth. The core of the Zuccale Previous HitFaultNext Hit is characterised by a distinct sequence of Previous HitfaultNext Hit rocks, including a heterogeneous assemblage of foliated phyllites. Preliminary fieldwork has highlighted the importance of high-angle footwall structures, present throughout the history of the main Previous HitfaultNext Hit, in controlling the internal distribution of Previous HitfaultNext Hit rocks. Footwall extension was achieved along early flat-lying cataclastic shears, followed by sequential high-angle normal faulting and Previous HitfaultNext Hit rotation. Future work will focus on quantifying conditions of deformation within the Previous HitfaultNext Hit zone, the permeability structure of the Previous HitfaultTop core, and on understanding the role of fluid flow.

AAPG Search and Discovery Article #90060©2006 AAPG Foundation Grants-in-Aid