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Lunar–solar periodicities of large earthquakes in southern California


Large earthquakes in southern California with epicentres between 33 and 36° N have statistically significant 12-hourly, lunar fortnightly and 18.6-yr periodicities. Smaller earthquakes in the same region do not display these periodicities. A search for tidal effects associated with these periodicities shows that large earthquakes have significant correlations with the times and orientations of daily/semi-daily tidal stresses while the lunar fornightly term is associated with the ocean tides along the southern Californian coast.

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Kilston, S., Knopoff, L. Lunar–solar periodicities of large earthquakes in southern California. Nature 304, 21–25 (1983).

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