Low-effective fault strength of a blind detachment beneath the Indo-Burmese Arc (NE-India) induced by frictional–viscous flow.

We present evidence for frictional–viscous flow (or steady creep) behaviour of the blind detachment below the Indo-Burmese wedge (IBW), as characterised by the fault gouge exposed along the Churachandpur–Mao Fault, which is one of the splay faults to the blind detachment. The petrography of the exhumed phyllonitic gouge material (considered the wedge material from the detachment and representative of the detachment) indicates evidence of pressure solution and viscous flow. We use a microphysical model involving frictional–viscous flow, and together with microstructural observations from the exhumed gouge we interpret low shear strength (<20 MPa) within the frictional–viscous transition zone. The results of the model also suggest that the geodetically estimated strain rate in this region lies in the domain of steady creep or velocity strengthening frictional behaviour. We suggest that the presence of phyllosilicate-rich rocks may significantly weaken mature fault cores along the detachment beneath the IBW and facilitate frictional–viscous flow at shallow depth. This new evidence suggests a significantly reduced seismic hazard across the megathrust. Research Highlights: Frictional–viscous flow along the blind detachment beneath the Indo-Burmese Arc. Exhumed fault gouge indicates evidence of pressure solution and viscous flow. Phyllosilicate rich rocks significantly weaken mature fault cores along this detachment. Microphysical model imply low shear strength of the blind detachment. [ABSTRACT FROM AUTHOR]