Extended friction to flow laws and their applications to fault models and earthquake modeling across the lithosphere

Thursday, 18 December 2014
Toshihiko Shimamoto, Institute of Geology, China Earthquake Administration, Beijing, China and Hiroyuki Noda, JAMSTEC Japan Agency for Marine-Earth Science and Technology, Kanagawa, Japan
Establishment of a constitutive law from friction to high-temperature plastic flow has long been a task for solving problems such as modeling earthquakes and plate interactions. Here we propose an empirical constitutive law that describes this transitional behavior using only friction and flow parameters, with good agreements with experimental data on halite shear zones. The law predicts a complete spectrum of steady-state and transient behaviors, including the dependence of the shear resistance of a fault on slip rate, effective normal stress and temperature. The law predicts a change in velocity-weakening to velocity-strengthening with increasing temperature, very similar to the change recognized for granite under hydrothermal conditions. It is surprising that a slight deviation from the steady-state friction law due to the involvement of plastic deformation can cause a large change in the velocity dependence. We solved seismic cycles of a fault across the lithosphere with the friction to flow law using a 2D spectral boundary integral equation method, revealing dynamic rupture extending into the aseismic zone and very rich evolution of interseismic creep including slow slip prior to earthquakes. Seismic slip followed by creep is consistent with natural pseudotachylytes overprinted with mylonitic deformation. Our friction-to-flow law merges “Christmas-tree” strength profiles of the lithosphere and rate-dependency fault models used for earthquake modeling on a unified basis. Conventionally strength profiles were drawn assuming a strain rate for the flow regime, but we emphasize that stress distribution evolves reflecting the fault behavior. A fault-zone model was updated based on the earthquake modeling.