Shear Image (IMAGE) Penn State Caption Scanning electron microscope images of laboratory fault zone showing sense of shear (white arrows) and zones of localized shear. Slow stick-slip is thought to originate when failure begins on one of these surfaces, but is partially arrested as slip velocity increases and the friction behavior changes from potentially unstable, velocity weakening frictional behavior to stable, velocity strengthening frictional behavior. Credit Haines, S. H.; Kaproth, B.; Marone, C.; Saffer, D. and B. A. van der Pluijm Usage Restrictions Non commercial use only License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.