Localised and distributed deformation in the lithosphere: the example of the Dead Sea valleys

The Earth’s lithosphere can be regarded as a strain softening elasto-plastic material. In the lab, such materials have been shown to deform in a brittle or a ductile manner depending on the applied geometric boundary conditions. Deformation in the lithosphere is usually thought to depend only on pressure, temperature and material composition with variations of these parameters determining the deformation style but the importance of boundary conditions has been largely ignored. By taking deformation associated with the Dead Sea (Jordan and Araba) valleys as an example, we demonstrate how boundary conditions control the deformation style causing some deformation to localise on a through-going strike-slip fault (~ 65%) but also requiring deformation associated with valley opening and change of valley strike to remain distributed (~35%). We show that while faults become weak, zones of distributed deformation remain strong and dissipate most energy. These results change dramatically our view of the deformation of the lithosphere, the strength of plate boundaries and more generally of the deformation of strain softening elasto-plastic materials.