(NAS Colloquium) Earthquake Prediction The Scientific Challenge (1996) / Chapter Skim
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A selective phenomenology of the seismicity of Southern California
A selective phenomenology of the seismicity of Southern California
Pages 3756-3763
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From page 3756... ...
We summarize the observational data of the fluctuations of seismicity in space, in time, and in a coupled space-time regime over the past 60 yr in Southern California, to provide a basis for determining whether these fluctuations are correlated with the times and locations of future strong earthquakes in an appropriate time- and spacescale. The simple extrapolation of the G-R distribution must lead to an overestimate of the risk due to large earthquakes.
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From page 3757... ...
In this model, these characteristic fault segments have characteristic slips in large earthquakes. But a process of repeated slip between strong barriers must ultimately accumulate stress at the barrier edges, and the barriers in this model must ultimately break as well; under the constraint of a long-term average uniform slip rate at every point in a plate boundary, barriers cannot remain unbroken forever.
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From page 3758... ...
Although it is possible that there might be a shift in style of seismicity from one that favors exclusivity of large earthquakes to one that favors a broad distribution of sizes on the SAF, some numerical simulations of seismicity on single faults with configurations of fracture thresholds that have been designed to favor the characteristic earthquake model have exhibited abrupt changes in size of earthquakes by factors that are much smaller than the range demanded by these speculations. Large earthquakes on neighboring faults produce significant fluctuations in stress on the SAF and vice versa and influence the mode of self-organization under the conditions of stress redistribution.
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From page 3759... ...
The probability of a strong earthquake occurring on any specific fault other than the SAF is finite but small; the probability of occurrence of a strong earthquake with magnitude M = 7 is significantly higher than that of an earthquake with M = 8. The modeling demands are stupendous, especially in view of the fact that mapping has not yet identified most of the faults that support strong earthquakes of the Northridge or Landers types, in a network that we estimate to include as many as several hundred faults.
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From page 3760... ...
has given an excellent review of space-time-coupled fluctuations: quiescence or reduced activity has been identified prior to 41 very strong earthquakes worldwide out of a list of 52 earthquakes, over a time scale of a few months to as much as 30 yr, and over distance scales that are usually of the order of the dimensions of the fracture of the strong earthquake. Wyss and Habermann (44)
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From page 3761... ...
(~50') propose that the faults in Southern California that undergo more frequent rupture, such as the SAF and the San Jacinto fault, tend to have much lower stress drops than do the faults that support less frequent events, implying that the healing process is gradual.
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From page 3762... ...
Probably the most alluring proposal for intermediate-term earthquake prediction is the idea that local quiescence of small earthquakes develops near the site of a future strong earthquake and that intermediate magnitude activity increases at distance from the future earthquake. The most likely candidate for modeling the fluctuations in stress drops and fracture thresholds is an asperity model for individual earthquakes and a barrier model that accounts for the complexity of the fault network.
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From page 3763... ...
(1981) Earthquake Prediction: An International Review, eds.
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