Fig. 1: Experimental setup, shear strength evolution, and fault structure development.
From: Spontaneous complexity in the dynamics of slow laboratory earthquakes
a Double direct shear arrangement with two fault zones, a transparent central block, and a camera to capture images of the inner fault surface (XY plane). b Friction and average fault surface luminosity during shear deformation at constant LPV = 10 µm/s. c Snapshots of the fault surface luminosity showing spatiotemporal evolution of luminosity during shear. Temporal sequence of snapshots is given in (b). Riedel R1 shears begin to form after the peak stress (grey box in panel (b)). They form first at the bottom (white arrow) and then progressively above as slip accumulates. Higher-stressed areas appear darker. The black arrow indicates subsidiary R-shears forming through lateral extrusion of the sample. Dashed region in VIII: area analysed in Figs. 2 and 3. Video version of panel (c) in Supplementary Movies 1 and 2.
