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Predicting Earthquakes A Scientific and Technical Evaluation, With Implications for Society (1976) / Chapter Skim
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Methods of Attempting Prediction
Pages 9-14

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From page 9...
... A number of earthquakes sufficiently large for statistical inference may be tabulated for a large area over a short time interval or for a small area over a long interval, but seldom are data available in adequate numbers for a small area over a short time interval. For example, the worldwide locations of earthquakes for only a short interval of time (Figure l)
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From page 10...
... • 0 0 -rf z Oil w » 01 w m 8 .
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From page 11...
... Much of the time, non-randomness is due to aftershocks that are known to be clustered in a short time interval following the parent event. When aftershocks are removed from the Southern California catalogue so that only a residual catalogue of large events remains (i.e., aftershock-producing events)
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From page 12...
... But, in general, in order to make up for the lack of comprehensive long-term historical records in the United States and in other parts of the world, we must improve statistical analysis by taking geophysical models into account. GEOPHYSICAL METHODS Geophysical methods involve searching for, identifying, and monitoring changes in the physical state of the earth that are precursory to earthquakes.
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From page 13...
... By reviewing seismic records for the period preceding the San Fernando earthquake of February l97l, it was later found that this earthquake was preceded by similar anomalous seismic velocity ratios. Since then, anomalous changes in tilt directions, variations in radon concentration in ground water, variations in compressional velocity, anomalous magnetic fields, anomalous electrical resistivity, the relative abundances of large and small earthquakes, and the overall level of seismic activity have all been proposed, and on occasion used, either to forecast or "hindcast" earthquakes.
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From page 14...
... It has been proposed that these dilatancy models can explain the wide variety of observed precursory phenomena, including changes in seismic velocity and electrical resistivity, land uplift and tilt, fluid flow, rate of radon emanation, frequency of occurrence of small earthquakes, and the relative abundance of large and small earthquakes. As yet, only the roughest of linkages exist between the models of precursory phenomena and observations of them in the field.
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Key Terms

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  • velocity ratio

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  • electrical resistivity

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  • methods geophysical
  • historical time
  • anomalous seismic

  • evident precursory
  • throughout historical
  • rock dilatancy
  • space usually
  • anomalous magnetic

  • geophysical models
  • historical accounts
  • methods shown
  • improve statistical
  • physically anomalous

  • region immediately
  • statistical inference
  • scientists observed
  • anomalies observed
  • seismic activity


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