9316082 Marone The PI will perform experiments to determine the critical slip distance, which plays a key role in determining the rupture nucleation dimension, the magnitude of the precursive moment release, and the maximum seismic ground acceleration. He will measure this parameter for a wider range of materials, normal stresses, and slip rates than previous studies, will investigate in detail the frictional behavior and constitutive parameters for shear within fractally-rough surfaces, and will systematically model the data collected. In this way, he will develop an understanding of the underlying mechanics and physical processes, and investigate how these mechanics and processes relate to those operative in natural fault zones. ****