[1] Knowledge of the spatial extent of damage surrounding fault zones is important for understanding crustal fluid flow and also for understanding the physical processes and mechanics by which fault zones develop with slip. There are few data available on the scaling of the fault damage zone with fault displacement, and of those that exist, deriving scaling relationships is hampered by comparing faults that run through different lithologies, have formed at different crustal depths or tectonic regimes (e.g., normal versus strike-slip movement). We describe new data on the microfracture damage zone width from small displacement fault zones within the Atacama fault zone in northern Chile that formed at ∼6 km depth within a dioritic protolith. The microfracture damage zone is shown by an alteration halo surrounding the faults in which the density of the microfractures is much greater than background levels in the undeformed protolith. The data show that damage zone width increases with fault displacement and there appears to be a zero intercept to this relationship, meaning that at zero displacement, there is no microfracture damage zone. This is supported by field observations at fault tips that show a tapering out of fault damage zones. These data, combined with data from the literature, indicate that this same relationship might hold for much larger displacement faults. There is also a distinct asymmetry to the fracture damage. Several processes for the development of the observed scaling are discussed. The widely accepted theory of a process zone predicts that fault damage zone width increases with fault length and thus should always be largest at a propagating fault tip where displacement is lowest. This prediction is opposite to that seen in the current data set, leading to suggestion that other processes, such as damage zone growth with increasing displacement due to geometric irregularities or coseismic damage formation might better explain the spatial extent of damage surrounding even low-displacement faults.Citation: Faulkner, D. R., T. M. Mitchell, E. Jensen, and J. Cembrano (2011), Scaling of fault damage zones with displacement and the implications for fault growth processes,

A free-field recording of the Denali fault earthquake was obtained by the Alyeska Pipeline Service Company 3 km from the surface rupture of the Denali fault. The instrument, part of the monitoring and control system for the trans-Alaska pipeline, was located at Pump Station 10, approximately 85 km east of the epicenter. After correction for the measured instrument response, we recover a seismogram that includes a permanent displacement of 3.0 m. The recorded ground motion has relatively low peak acceleration (0.36 g) and very high peak velocity (180 cm/s). Nonlinear soil response may have reduced the peak acceleration to this 0.36 g value. Accelerations in excess of 0.1 g lasted for 10 s, with the most intense motion occurring during a 1.5-s interval when the rupture passed the site. The low acceleration and high velocity observed near the fault in this earthquake agree with observations from other recent large-magnitude earthquakes. [DOI: 10.1193/1.1778172

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