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The Shear Deformation Zone and the Smoothing of Faults with Displacement
  • Clement Perrin,
  • Felix Waldhauser,
  • Christopher H. Scholz
Clement Perrin
Institut De Physique Du Globe De Paris

Corresponding Author:clem.perrin@gmail.com

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Felix Waldhauser
Lamont-Doherty Earth Observatory of Columbia University
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Christopher H. Scholz
Lamont-Doherty Earth Observatory
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Abstract

We use high-resolution earthquake locations to characterize the three-dimensional structure of active faults and how it evolves with fault structural maturity. We investigate the distribution of aftershocks of several recent large earthquakes that occurred on crustal strike slip faults of various structural maturity (i.e. various cumulative fault displacement, length, initiation age and slip rate). Aftershocks define a tabular zone of shear deformation surrounding the mainshock rupture plane. Comparing this to geological observations, we conclude that this results from the re-activation of secondary faults. We observe a rapid fall off of the number of aftershocks at a distance range of 0.06-0.25 km from the main fault surface of mature faults, and 0.7-1.5 km from the fault surface of immature faults. The total width of the active shear deformation zone surrounding the main fault plane reaches ~1.5 km and 2.5-6 km for mature and immature faults, respectively. We find that the width of the shear deformation zone decreases as a power law with cumulative fault displacement. Comparing with an existing dynamic rough fault model, we show that the narrowing of the shear deformation zone agrees quantitatively with earlier estimates of the smoothing of faults with displacement, both of which are aspects of fault wear. We compare this evolution of fault structure with several attributes of earthquakes, and find that earthquake stress drop decreases with fault displacement and hence with increased smoothness.