(NAS Colloquium) Earthquake Prediction The Scientific Challenge (1996) / Chapter Skim
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Slip complexity in earthquake fault models
Slip complexity in earthquake fault models
Pages 3811-3818
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From page 3811... ...
Models based on classical friction laws without a weakening length scale or for which the numerical procedure imposes an abrupt strength drop at the onset of slip have he = 0 and hence always fall into the inherently discrete class. We suggest that the small-event complexity that some such models show will not survive regularization of the constitutive description, by inclusion of an appropriate length scale leading to a finite he,, and a corresponding reduction of numerical grid size.
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From page 3812... ...
The friction model incorporates the observed displacementdependent features of friction as in rate- and state-dependent frictional constitutive laws. Such assures that numerical fault models have a well-defined limit with refinement of the computational grid (5~; the same is not necessarily the case with modeling based on classical friction laws without gradual displacement-dependent features of strength transition.
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From page 3813... ...
, p and T are variable. Some Simulation Results and Implications for Complexity We find that all smooth fault models as thus far examined in our simulations fail to produce complex slip sequences like those of realistic G-R F-S statistics of earthquakes, at least for events with a maximum rupture dimension that is comparable to or less than the seismogenic depth.
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From page 3814... ...
We think the large event complexity in the model using the ageing friction law may reflect saturation of the growth of stress concentration at a rupture front, with increase of rupture dimension, for events larger than the seismogenic thickness. We do not yet know why the same fails to stop ruptures and complexity with the slip law.
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From page 3815... ...
Strong velocity weakening at high rates is also of interest as a possible mechanism, among others, allowing fault operation at low overall driving stresses. A common feature of smooth fault models is that the growing stress concentration at a rupture tip is so strong that ruptures become unstoppable, at least until the growth of stress concentration with rupture size saturates at seismogenic dimensions.
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From page 3816... ...
A narrow range of size scales, as for mature highly slipped fault zones, leads to quasi-periodic recurrence and characteristic large events, a response generally compatible with the seismic gap hypothesis. Our discrete fault models with 3D elastic stress transfers generate, typically, discontinuous rupture areas.
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From page 3817... ...
These include G-R F-S distribution of small events, enhanced frequency of large events resembling the characteristic earthquake distribution for models with a narrow range of size scales, extended range of power-law F-S statistics for models with a wide range of size scales, noncontiguous rupture areas, and repeating small events near locked zones. Models based on classical friction laws with L = 0, or which adopt solution algorithms with imposition of abrupt strength drops, have nucleation size he = 0, so they are automatically in the inherently discrete class.
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From page 3818... ...
have been based on a cellular basis set for the slip distribution, making it spatially uniform within rectangular cells and enforcing the constitutive law in terms of the stresses at cell centers. The mirror symmetry condition of the spectral formulation causes the shear-free conditions Ax, y, 0, t)
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