Predicting Earthquakes A Scientific and Technical Evaluation, With Implications for Society (1976) / Chapter Skim
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Current Capability for Earthquake Prediction in the United States
Current Capability for Earthquake Prediction in the United States
Pages 15-23
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From page 15... ...
was part of the Nuclear Test Detection Program of the Advanced Research Projects Agency of the Department of Defense. The Nuclear Test Detection Program in many ways converted seismology into a modern observational science, using arrays of seismic detectors, digital processing of data, and the application of information theory in signal processing.
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From page 16... ...
engineeringseismological investigations. Successful projects to date include the establishment of a joint seismograph network near Garm, Tadzhik SSR, to search for seismic forerunners to larger earthquakes; the establishment of a joint seismograph network around the Nurek Reservoir, Tadzhik SSR, to study reservoir-induced seismicity; the study of the spectral content of earthquakes using the Soviet "frequency-selecting" seismograph system and American broad-band, digitally recording equipment; collaborative laboratory studies of the effects precursory to failure and sliding in rock samples; the application of pattern-recognition techniques to the prediction of earthquakes; the establishment of a joint strong-motion network in the Tadzhik SSR; and the collaborative instrumentation and testing of buildings subjected to earthquake-like motions simulated by explosions.
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From page 17... ...
In particular, strainmeters, geochemical monitoring instrumentation, and 3 wave-length electro-optical ranging devices, among others, still require some development. New instruments that yield great improvement in resolution have also been proposed and may ultimately prove useful, especially if they can be installed at adequate depth to remove environmental noise effects.
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From page 18... ...
LABORATORY STUDIES Most of the conceptual underpinnings of the physical models now used to explain earthquake precursors derive from laboratory experiments. Dilatancy and precursory fault creep, both instabilities that lead to failure, were observed in the laboratory long ago.
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From page 19... ...
The subject is an important one, however, because deformation of the lower crust and uppermost mantle is involved in large earthquakes. Most current research focuses on the details of the failure process preceding brittle fracture, which is, in effect, the "laboratory earthquake." Dilatant cracking and fault creep precede the sudden failure, and accelerate unstably very near the time of fracture.
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From page 20... ...
Physical models of the response of materials to low stresses, in both high- and low-temperature regimes, will help determine the amount of intraplate strain accumulation as well as the motions of the earth in the region vertically below active zones of shallow earthquake faulting, as in California. Are the present rheological models, often obtained from steady-stress laboratory experiments, applicable to the transient physical changes that characterize earthquakes, and to the associated slower creep motions of the regions far from the active fault zones?
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From page 21... ...
Do intraplate earthquakes indicate the presence of inhomogeneous stress fields at distances of a few hundred kilometers or more from major fault zones, or can these events be ignored in the modeling of major fault zones such as the San Andreas? Information about the relative motions within and between plates can be obtained by long-range geodetic studies, such as very-long-base-line interferometry, multilateration techniques, etc.
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From page 22... ...
Most of the data on changes in electrical resistivity, radon emanation, changes in water level in wells, and changes in land elevation come from these three countries. As another example, basic research during the last l5 years on flow of fluids in porous media, crack propagation, dilatancy, and physical properties of rocks has played a pivotal role in development of current theories of the physical basis for precursory effects of earthquakes, but much is still unknown.
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From page 23... ...
It is extremely important that such instruments be installed in many of the seismic areas of the United States, including, for example, the area of current anomalous uplift near Palmdale, California. In particular, it is important to establish several small arrays, with dimensions of about one kilometer, that would include several types of strain- and tilt-measuring instruments, as well as to perform repeated geodetic leveling of the array.
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