Mechanical behavior and the degree of localization in large displacement faulting experiments

1. Mechanical behavior and the degree of localization in large displacement faulting experiments N. M. Beeler and T. E. Tullis, Brown University, Providence, RI (2) 1 mm (4) 1 mm [Chester et al.., 1993] 2 to 4 km depth, g=d/w=508 (Chester et al., 1993)

2. Deformation and mechanical behavior large displacement faulting experiments 1.Description of experiments and conditions - intially bare surfaces - gouges 2. Granite: Textures and mechanical behavior 3. Implications for seismic faulting 4. General conclusions { Power et al., 1989; Yund et al., 1990 Beeler et al., 1996 Blanpied and Beeler, 1998

3. Conditions in experiments: dry, room temperature

4. Measurements rate dependence of strength (e.g., Dieterich 1978;1979) velocity weakening velocity strengthening dilatancy (e.g., Morrow and Byerlee, 1989; Marone et al., 1990)

5. Fault configurations

6. Initially bare surfaces

7. d=376mm, g=4800, ~ 60% amorphous material [Yund et al., 1990],tc=0.62MPa

8. g=10 g=1000 natural faulting oops, too much strain! (from Power et al., 1989)

9. Simulated gouge

10. (from Beeler et al., 1996) d=10 mm, g=13

11. (from Blanpied and Beeler, 1998) d=65 mm, g=75

12. d=194 mm, g=255 (from Blanpied and Beeler, 1998)

13. d=407 mm, g=530 (from Blanpied and Beeler, 1998)

14. Subcritical fracture growth (Charles and Hillig, 1962) (Atkinson, 1987) (also see Scholz, 1968; Das and Scholz, 1981)

15. Characteristics of seismic failure in the laboratory (from Beeler and Lockner, 2002) Simple friction or fracture based relation for seismic failure Dieterich, 1992 Lockner, 1998 Marcellini, 1995 Shaw, 1993 Atkinson, 1984 Das and Scholz, 1981 Knopoff, 1969 Scholz, 1968 Griggs, 1940

16. Implications of delayed failure: Earthquake occurrence insensitive to periodic stress of periodless than the delay time Predicted duration of earthquake nucleation (Dieterich, 1994) = 10MPa/75 yr a =0.0045 sn=18MPa/km Depth 5 - 15 km tn= 11 - 33 days Lab-based prediction: earthquake occurrence should not correlate with the passage of seismic waves and daily earthtides

17. Summary of laboratory observations: Deformation in laboratory faulting experiments is accommodated by rigid rotation, sliding between particles and grain fracture. Grain-size reduction from fracture accompanies shear localization Shear localization is required for seismic faulting Seismic failure is delayed, defining a duration of nucleation Conclusions: Fault deformation during and prior to earthquake occurrence involves grain- scale fracturing The duration of nucleation for earthquakes is long (> 1 week) Duration is likely due to short term non-linear viscous effect from sub-critical fracture growth