Stick-slip failure in sheared fault with a variety of end constraint degrees: An experimental study

For the commonly-used laboratory frictional earthquake model, unstable slip usually occurs without any end constraint. This experimental design is contradictory to a simple fact: real faults are confined by their surroundings, and the relative sliding is not end-free. To investigate the effects of end constraint conditions on the stick-slip behaviors, direct shear tests are conducted on PMMA sheets with three kinds of pre-crack length, and high sampling rate strain gage array and digital image correlation method are used to monitor the detailed processes of dislocation(stick-slip). We find that pre-crack length has great influence on the intervals of dislocation (stick-slip), the total number of dislocations (stick-slip) that occurs before crack extension, the magnitude of stress-drop and rupture velocity. A transition of the dislocation propagation velocity from sub-Rayleigh to super-shear is observed for PMMA sheets with a long pre-crack, while super-shear velocity rupture cannot be obtained in PMMA sheets with a short pre-crack.