The dependence of the dry friction threshold on rupture dynamics
  The static friction coefficient between two materials is considered to be a material constant. We present experiments demonstrating that the ratio of shear to normal force needed to move contacting blocks can, instead, vary systematically with controllable changes in the external loading configuration. Large variations in both the friction coefficient and consequent stress drop are tightly linked to changes in the rupture dynamics of the rough interface separating the two blocks. 
Oded Ben-David and Jay Fineberg
cond-mat.mtrl-sci physics.geo-ph