Letter | Published:

Fluctuations of seismicity before major earthquakes

Naturevolume 266pages710712 (1977) | Download Citation



LONG-TERM precursory changes of seismicity previously reported are (1) a change in the relationship between earthquake frequency and magnitude, and (2) a decrease in the frequency of micro-earthquakes. In a review of earthquake precursors Rikitake1 cites eleven examples of the former and three examples of the latter. On the dilatancy hypothesis a decrease in activity is to be expected from dilatancy hardening2; an earlier gradual increase of activity due to the secular increase of tectonic stress was also postulated2. A more distinctive sequence of seismicity fluctuations can be recognised from data in seismological bulletins. The fluctuations are large: a burst of activity marking the start of the precursory sequence is followed by a period of abnormal quiet, and this lasts until the onset of the major event. We report here characteristic changes of minor earthquake activity, preceding a number of recent major earthquakes in regions with good seismographic coverage, and suggesting a new basis for long-term prediction relying directly on the normal data output of permanent seismograph networks.

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  1. 1

    Rikitake, T. Bull seism. Soc. Am. 65, 1133–1162 (1975).

  2. 2

    Scholz, C. H., Sykes, L. R. & Aggarwal, Y. P. Science 181, 803–810 (1973).

  3. 3

    Coffman, J. L. & Cloud, W. K. United States Earthquakes 1968 (U. S. Department of Commerce, 1970).

  4. 4

    New Zealand Seismological Report 1961–1973 (Geophysics Division, DSIR, Wellington).

  5. 5

    Hileman, J. A., Allen, C. R. & Nordquist, J. M. Seismicity of the Southern California Region 1 January 1932 to 31 December 1972 (Seismological Laboratory, California Inst. of Technology, 1973).

  6. 6

    Evison, F. F., Robinson, R. & Arabasz, W. J. N. Z. Jl Geol. Geophys. 19, 625–637 (1976).

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  1. Institute of Geophysics, Victoria University of Wellington, Wellington, New Zealand

    • F. F. EVISON


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