Stress control of frictional hangingwall accommodation above thrust ramps

Résumé

Experimental models are used to study the stress control of frictional hangingwall accomodation above rigid flat-ramp-flat footwalls. Hangingwall accommodation involves shear or kink-band nucleation above the lower fault bend and migration of these as the hangingwalls climb over the underthrusting footwall. The kinkbands change shape and localise to thrusts as they migrate over the flat-ramp-flat footwall. When the shear stress to gravity stress ratio is low the thrusts reactivate to normal faults. With increase in the shear stress to gravity stress ratio reactivation of the kink bands was by tensile failure, at the upper fault bend. The models show that by changing the strength of materials deforming under otherwise similar conditions it is possible to study the geometry of frictional hangingwall accommodation, at different scales. In nature, hangingwall accommodation by thrust nucleation above thrust ramps and their subsequent normal reactivation may be anticipated in frictional sediments at shallow crustal levels, where temperatures and pressures are low.