Fault Friction, Plate Rheology, and Mantle Torques From a Global Dynamic Model of Neotectonics

Abstract Improvements in software, parallel computing, global data sets, and laboratory flow‐laws help to develop the global Earth5 thin‐shell finite‐element model of Bird et al. (2008, https://doi.org/10.1029/2007jb005460 ) into a benchmark study. All experiments confirm that modeled faults (other than megathrusts) have low effective friction of 0.085 ± 0.034. The average down‐dip integral of shear traction on subduction megathrusts is 1.3 ± 0.2 × 10 12 N/m. In plate interiors the dislocation‐creep flow‐law for continental crust is about twice as strong as granodiorite; close to diorite. Upper‐mantle creep strength is close to olivine‐rich peridotite in both oceanic lithosphere and continents. “Byerlee's law” friction of 0.85 applies between active faults in both oceanic lithosphere and stable continents. Computed net slab‐pull on subducting plates is typically comparable to ridge‐push, but ranges to 5× larger; slab‐pull moves the plate toward the trench (6 cases) or is neutral (1 case). Under the 6 largest plates with no attached slabs, basal tractions are 0.1∼1.2 MPa. Implications for Earth mechanics include: (a) Plate‐boundary faults are weakened by low‐friction minerals in oceanic transform faults, temporary coseismic pore pressure elevation in many continental transforms, and permanent high pore pressure in subduction megathrusts; (b) Such weak faults are rare in plate interiors, which display Byerlee's Law friction and dislocation creep strengths matching laboratory results; (c) Generally “forward” net slab pull and basal shear tractions help gravitational potential energy to drive the plates. Implications for future modeling include: (d) Fault elements are required; (e) Laboratory flow‐laws should replace Newtonian viscosity; and (f) Mohr‐Anderson friction should replace isotropic plasticity.