Dynamic models of interseismic deformation and stress transfer from plate motion to continental transform faults

Abstract

[1] We present numerical models of earthquake cycles on a strike-slip fault that incorporate laboratory-derived power law rheologies with Arrhenius temperature dependence, viscous dissipation, conductive heat transfer, and far-field loading due to relative plate motion. We use these models to explore the evolution of stress, strain, and thermal regime on "geologic" timescales ($10 6 -10 7 years), as well as on timescales of the order of the earthquake recurrence ($10 2 years). Strain localization in the viscoelastic medium results from thermomechanical coupling and power law dependence of strain rate on stress. For conditions corresponding to the San Andreas fault (SAF), the predicted width of the shear zone in the lower crust is $3-5 km; this shear zone accommodates more than 50% of the far-field plate motion. Coupled thermomechanical models predict a single-layer lithosphere in case of "dry" composition of the lower crust and upper mantle, and a "jelly sandwich" lithosphere in case of "wet" composition. Deviatoric stress in the lithosphere in our models is relatively insensitive to the water content, the far-field loading rate, and the fault strength and is of the order of 10 2 MPa. Thermomechanical coupling gives rise to an inverse correlation between the fault slip rate and the ductile strength of the lithosphere. We show that our models are broadly consistent with geodetic and heat flow constrains from the SAF in Northern California. Models suggest that the regionally elevated heat flow around the SAF may be at least in part due to viscous dissipation in the ductile part of the lithosphere.Citation: Takeuchi, C. S., and Y. Fialko (2012), Dynamic models of interseismic deformation and stress transfer from plate motion to continental transform faults,

Shear strain concentration mechanism in the lower crust below an intraplate strike-slip fault based on rheological laws of rocks

“…6c). Our result of temperature increase in model W30E is consistent with the results of recent thermo-mechanical models of interplate strike-slip faults (e.g., Takeuchi and Fialko 2012;Moore and Parsons 2015). The maximum temperature increase in the cases of wet rheologies is ∼200 °C, and the effective viscosity was significantly lowered by the increased temperature.…”

“…In the previous studies (e.g., Takeuchi and Fialko 2012;Moore and Parsons 2015), the temperature increase in the cases of dry rheologies is about 200 °C higher than that in the cases of wet rheologies. In our study, the effect of water on temperature increase is not significant because the maximum shear strain rate (Fig.…”

“…Observation of the broadly distributed heat flow anomaly on the San Andreas Fault (see Lachenbruch and Sass 1980) has been explained by shear heating in the lower crust. The temperature anomaly in the lower crust can reach several hundred degrees, which can create an observable heat flow anomaly on the surface (e.g., Thatcher and England 1998;Leloup et al 1999;Takeuchi and Fialko 2012). A large temperature anomaly can result in a weak zone with low seismic velocity that can be observed as a heterogeneous velocity structure in the seismic tomography data (Wittlinger et al 1998).…”

Shear heating-induced strain localization across the scales

“…Moreover, theses thicknesses can be estimated using Equation (17), which is only controlled by physical parameters (see [9] for more details). Similar resolution independent strain localization Downloaded by [New York University] at 04:50 16 July 2015 behaviour has been confirmed by other authors such as [40] using a mesh-free method and [29,41] with the finite element method.…”

The earthquake deformation cycle

“…This approach is challenging because the knowledge needed to make such a prediction is imperfect, and the resulting models are complex, involving variations in material properties and physical conditions in space and time. The most comprehensive attempt to produce such a model is from Takeuchi and Fialko (2012). For realistic geological materials, they find that strain localises in the viscoelastic substrate due to shear heating and the power-law dependence of strain rate on stress, effectively producing a weak zone under the fault that is able to relax quickly during the postseismic period.…”