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Episodic fault creep events in California controlled by shallow frictional heterogeneity


In the uppermost 3–5 km of continental strike-slip faults, a significant fraction of the total slip is typically accommodated by stable sliding, or fault creep. Creep can be continuous or episodic, lasting only a few hours, and varies throughout the earthquake cycle and from one fault to another1,2,3. The most commonly used mechanical model4 attributes episodic creep events to the transition from unconsolidated sediments to lithified rocks at depth. However, this model cannot explain the wide variability in observed shallow creep characteristics on strike-slip faults in California. Here, we use numerical simulations to examine a range of alternative mechanical models that can reproduce the variability of shallow creep behaviour in both postseismic and interseismic periods. We find that geodetic observations of creep behaviour on a number of significant fault segments in California are matched when an additional unstable layer is embedded within the shallow, stable zone. This layer may result from fine-scale lithological heterogeneities within the stable zone5,6—frictional behaviour varies with lithology, generating the instability. Our model suggests that the displacement of and interval between creep events are dependent on the thickness, stress and frictional properties of the shallow, unstable layer. We also suggest that such frictional heterogeneity may be the mechanism responsible for slow slip events in many subduction zones.

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Figure 1: Variability of surface fault creep in California.
Figure 2: Two schematic models that may explain the variability of surface fault creep.
Figure 3: Simulation results of Models A and B.
Figure 4: Dependence of fault displacement and interval of creep events on the thickness H of the shallow VW layer in Model B and geological loading rate.

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We thank H. Yang, C. Rowe and D. Kilb for helpful discussions. This work was done with the support of NSF grant EAR-0952174, OCE-1061203 and SCEC grant #12147. SCEC is funded by NSF Cooperative Agreement EAR-0529922 and USGS Cooperative Agreement 07HQAG0008. The SCEC contribution number for this paper is 1690.

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All authors contributed extensively to the work presented in this paper. Y.L. wrote the quasi-dynamic code. M.W. ran the simulations and analysed the results. Y.K. ran the fully dynamic simulations. J.J.M. supervised the project. M.W. drafted the manuscript and made all the figures. All authors discussed the results and implications and commented on the manuscript at all stages.

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Correspondence to Meng Wei.

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Wei, M., Kaneko, Y., Liu, Y. et al. Episodic fault creep events in California controlled by shallow frictional heterogeneity. Nature Geosci 6, 566–570 (2013).

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