(NAS Colloquium) Earthquake Prediction The Scientific Challenge (1996) / Chapter Skim
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Intermediate- and long-term earthquake prediction
Intermediate- and long-term earthquake prediction
Pages 3732-3739
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From page 3732... ...
I devote considerable attention to the quasi-periodic nature of large events that rerupture specific fault segments since that property bears strongly upon whether prediction of some kind is likely to be Abbreviations: M, earthquake magnitude; Mo7 seismic moment; New, moment magnitude; OFF, Coulomb failure function; NEPEC, National Earthquake Prediction Evaluation Council; W downdip width; L, rupture length; N
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From page 3733... ...
Solid circles, epicenters of 1906,1989, and 1868 earthquakes; heavy solid lines, rupture zones of those three large shocks; dashed lines enclose events taken to be within their precursory areas. Arrows in A denote sense of strike-slip motion along San Andreas fault.
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From page 3734... ...
One of the common features of large earthquakes along plate boundaries is that a fault segment may break by itself one time but in conjunction with one or more adjacent segments another time. The Loma Prieta segment of the San Andreas fault ruptured by itself in 1989, with the adjacent Peninsular segment in 1838, and with yet several additional segments to the north in 1906 (7, S)
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From page 3735... ...
A subsequent comparison of felt areas for the 1865 and 1989 shocks indicates that the former did not occur along the San Andreas fault (7~. Considerable debate ensued from 1984 until the Loma Prieta earthquake in October 1989 about the amount of displacement in 1906 along the southernmost 75 km of the 1906 rupture zone.
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From page 3736... ...
part of the Loma Prieta zone is encountered. They suggest that the orientation of the slip vector in the 1989 event, parallel to the line of intersection of the two fault segments, was not fortuitous and that it permits slip to occur on the two faults without opening subsurface voids.
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From page 3737... ...
I argued earlier that both are unlikely. Even if each event occurred on a different nearby fault, both involved substantial strike-slip motion and released shear strain energy, not from a fault surface, but from a volume of rock that extends outward about 75 km from each rupture zone.
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From page 3738... ...
Also, changes in stress generated by the Landers sequence of shocks resulted in portions of the fault in San Gorgonio Pass moving closer to failure by about 10 years (40~. The San Andreas fault undergoes a complex compressional left step in San Gorgonio Pass that is much larger than that in the Loma Prieta region.
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From page 3739... ...
If it had been realized that the Lake Elsman events were on a nearby but different fault, an intermediate-term warning would have been more appropriate. They probably indicated the return of stresses in that area to pre-1906 levels rather than the initiation of accelerated precursory slip on the San Andreas fault itself.
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