Off-fault tensile cracks: A link between geological fault observations, lab experiments, and dynamic rupture models
We examine the local nature of the dynamic stress field in the vicinity of the tip of a semi-infinite sub-Rayleigh (slower than the Rayleigh wave speed, c_R) mode II crack with a velocity-weakening cohesive zone. We constrain the model using results from dynamic photoelastic experiments, in which shear ruptures were nucleated spontaneously in Homalite-100 plates along a bonded, precut, and inclined interface subject to a far-field uniaxial prestress. During the experiments, tensile cracks grew periodically along one side of the shear rupture interface at a roughly constant angle relative to the shear rupture interface. The occurrence and inclination of the tensile cracks are explained by our analytical model. With slight modifications, the model can be scaled to natural faults, providing diagnostic criteria for interpreting velocity, directivity, and static prestress state associated with past earthquakes on exhumed faults. Indirectly, this method also allows one to constrain the velocity-weakening nature of natural ruptures, providing an important link between field geology, laboratory experiments, and seismology.
© 2012 by the American Geophysical Union. Received 10 June 2011; revised 4 November 2011; accepted 16 November 2011; published 20 January 2012. This manuscript benefited from comments and suggestions by the Associate Editor and two anonymous reviewers. Experiments were supported by the U.S. Geological Survey (USGS), Department of Interior, under USGS award 08HQGR0010 to Pollard. Griffith also received support under National Science Foundation (NSF) grant OISE-0754258. Rosakis and Ngo were supported by U.S. Department of Energy grant DE-FG52-06NA 26209, NSF grant EAR-0711545, and Office of Naval Research Multidisciplinary Research Initiative (ONR MURI) grant N0014-06-1-0730.
Published - Ngo2012p17160J_Geophys_Res-Sol_Ea.pdf