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Mechanical basis for slip along low‐angle normal faults
Author(s) -
Lecomte Emmanuel,
Le Pourhiet Laetitia,
Lacombe Olivier
Publication year - 2012
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2011gl050756
Subject(s) - geology , seismology , slip (aerodynamics) , magnetic dip , shear (geology) , extensional definition , brittleness , normal fault , fault (geology) , fault gouge , tectonics , petrology , geophysics , materials science , physics , composite material , thermodynamics
The existence of active low‐angle normal faults is much debated because (1) the classical theory of fault mechanics implies that normal faults are locked when the dip is less than 30° and (2) shallow‐dipping extensional fault planes do not produce large earthquakes (M > 5.5). However, a number of field observations suggest that brittle deformation occurs on low‐angle normal faults at very shallow dip. To reconcile observations and theory, we use an alternative model of fault reactivation including a thick elasto‐plastic frictional fault gouge, and test it at large strain by the mean of 2D mechanical modeling. We show that plastic compaction allows reducing the effective friction of faults sufficiently for low‐angle normal faults to be active at dip of 20°. As the model predicts that these faults must be active in a slip‐hardening regime, it prevents the occurrence of large earthquakes. However, we also evidence the neoformation of Riedel‐type shear bands within thick fault zone, which, we believe, may be responsible for repeated small earthquakes and we apply the model to the Gulf of Corinth (Greece).