Effects of Earthquake Recurrence on Localization of Interseismic Deformation Around Locked Strike-Slip Faults

Localized geodetic deformation of arctan shape around locked strike-slip faults is widely reported, but there are also important exceptions showing distributed deformation. Understanding the controlling mechanism is important to hazard assessment and geodynamic analysis. Here we use simple finite element viscoelastic earthquake cycle models to investigate the basic mechanics of this process. Our models feature a vertical strike-slip fault in an elastic layer overlying a viscoelastic substrate of Maxwell or Burgers rheology, with or without a low-viscosity shear zone representing deeper extension of the fault. We demonstrate that the primary control on the localization of interseismic deformation is the recurrence interval of past earthquakes. Given viscosity, shorter recurrence leads to greater localization, regardless of the rheological model used. The presence of a low-viscosity deep fault does not change this conclusion, although it tends to lessen localization by promoting faster postseismic stress relaxation. Distributed deformation, although less reported, is a natural consequence of very long recurrence and in theory should be as common as localized deformation. We think that the apparent propensity of the latter is likely associated with the much greater quantity and better quality of geodetic observations from higher-rate and shorter-recurrence faults. Our results also show the important role of nearby earthquakes along the same fault. For faults of relatively short recurrence, frequent ruptures of nearby segments, modeled using a migrating rupture sequence, further enhance localization. For faults of very long recurrence, faster near-fault deformation induced by a recent earthquake may give a false impression of localized interseismic deformation.