(NAS Colloquium) Earthquake Prediction The Scientific Challenge (1996) / Chapter Skim
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Nonuniformity of the constitutive law parameters for shear rupture and quasistatic nucleation to dynamic rupture: A physical model of earthquake generation processes
Nonuniformity of the constitutive law parameters for shear rupture and quasistatic nucleation to dynamic rupture: A physical model of earthquake generation processes
Pages 3795-3802
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From page 3795... ...
Data obtained from the high-resolution laboratory experiments enable one to discuss how unstable, dynamic shear rupture is nucleated in the brittle regime and its mechanical conditions in terms of the constitutive law for shear rupture in the framework of fracture mechanics. The breakdown zone and the nucleation zone will be modeled physically in terms of the constitutive law parameters, and it will be shown how well and physically reasonably the breakdown zone and the nucleation zone are scaled in terms of one of the constitutive law parameters, which in turn strongly depends on a characteristic length representing geometrical irregularities of the rupturing fault.
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From page 3796... ...
Thus, if there is a constitutive law applicable for shear rupture of any type, any phase, and any size scale, the law should primarily be slip dependent. A B xc SPY In to a, cn a' In Hi Da Dc Slip Displacement Shear Stress Breakdown ~ zone Shear crack ~/ l Xc 1 ~ ~ E :__ Dc Ala' ~ _ Distance Hip nor Tip of the breakdown zone Distance FIG.
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From page 3797... ...
To reveal local breakdown processes near the propagating tip of a shear rupture along the fault in rock of the brittle regime, and to get information on what specific functional form well represents the constitutive law for shear rupture, a number of high-resolution laboratory experiments (1-3, 12) have been performed on propagating shear rupture (mode II)
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From page 3798... ...
As mentioned above, the physically reasonable constitutive equation for shear rupture should result in the nonsingularity of not only the stresses but also the slip acceleration at or near the unstably and dynamically propagating tip of the rupture zone, because the unbounded acceleration is physically unreasonable. In fact, the bounded acceleration is crucial when strong motion source parameters, such as the peak slip acceleration, are discussed from a physical viewpoint.
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From page 3799... ...
By contrast, in shear rupture, the relative displacement is on the rupturing plane, and hence the rupturing surfaces are in mutual contact and interactive throughout the breakdown process. This shows that the size of the breakdown zone is affected by geometrical irregularities of rupturing surfaces and that the critical slip displacement is necessarily size-scale dependent, as demonstrated by the laboratory experiments.
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From page 3800... ...
develops with the rupture growth during the later phase of the nucleation process. By contrast, the size of the breakdown zone is almost constant in the zone of dynamic, fast-speed rupture propagation (Fig.
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From page 3801... ...
This leads to the conclusion that nonuniform distributions of the constitutive law parameters on the fault are necessary and sufficient conditions for creating the nucleation in the brittle regime. It has been shown that the shear rupture nucleation does occur in the brittle regime when the constitutive law parameters are distributed nonuniformly on the fault and that the size of the nucleation zone increases proportionally with Ac.
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From page 3802... ...
This strongly suggests that earthquake dynamic rupture is necessarily preceded by a quasistatic to quasidynamic nucleation process. However, whether or not a sizable zone of the nucleation appears prior to earthquake dynamic instability depends on how nonuniformly the constitutive law parameters prevail on the fault in the lithosphere (18~.
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