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Periods in earthquake activity^*

VILLA GRAL, MITRE (TOTORAL),, CÓRDOBA, ARGENTINA

Abstract

1. The extension of the 186-year period back to A.D. 0 is confirmed.

2. The presence also of an effective, probably composite, period of 93 years.

3. The periodic increase of activity, number of shocks, to a sharp maximum followed by a sudden and often nearly complete cessation of activity.

4. Double, very marked maxima with increasing separations, in double the 186-year period.

5. A high degree of homogeneity in these early records, and their entire suitability for exacting investigation.

6. The large number of lunar and lunar-solar periods present in seismic activity establish gravitation as in general the underlying cause of these ruptures.

7. Similarity of minor details which indicate the presence of other, shorter, lunar periods.

Footnotes

^* Manuscript received for publication March 22, 1948.