13th International Conference on Fracture June 16–21, 2013, Beijing, China -9- (a) (b) Figure 4 (continued). The sequence of snapshots of the τmax stress field induced by the (a) vertical and (b) nonvertical dip-slip faulting. As in Fig. 3, the rupture, initiated at depth at t = 0, propagates upwards but now it breaks the free surface. In (a), upon fault surfacing, four surface-types waves are generated: The Rayleigh pulses (waves) (marked as R) move along the free surface into the far-field and the interface pulses (I) propagate downwards along the ruptured fault surfaces. At a later stage (t = 8.7), the interface pulses merge into a shear wave. In (b), the wave energy trapped in the hanging wall is identifiable as a Rayleigh pulse Rh and the corner wave C. Strong dynamic disturbance may be found in the hanging wall behind the corner wave while in the footwall the induced stresses are relatively small. (a) (b) Figure 5. The experimentally obtained snapshots of isochromatic fringe patterns showing the typical dynamic wave field induced by fracture of an interface inclined at an angle of 45 degrees to the free surface. The photographs are taken at (a) 40 and (b) 280 µs after the incidence of the projectile, respectively. (a) -1.5 -1 -0.5 0 0.5 1 1.5 0 5 1015202530 Time [ms] Displacement [mm] (b) -1.5 -1 -0.5 0 0.5 1 1.5 0 5 1015202530 Time [ms] Displacement [mm] Figure 6. Typical particle displacements measured on the free surface associated with surface-breaking interface fracture, (a) on the hanging wall and (b) on the footwall (nonvertical case, time is zero when dynamic motion is detected for each diagram). 8.7 8.7 S C Sf R R Rh Rf 25 mm
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