Periodicity of earthquakes and the invariance of the gravitational constant

Times of occurrence for a total of 1933 earthquakes are analyzed for periodicities. The results show no definite evidence for effects due to earth tides. Small indications of a solar-date periodicity are assumed to be thermal in origin. A strong, statistically significant annual period is found, and the phase is substantially the same for northern and southern earthquakes. This periodicity is not wholly accounted for by temperature effects, wind-induced stresses, and observer bias. The occurrence of this periodicity would be understandable if the gravitational constant were to vary as the earth-sun distance changes or as the earth's velocity relative to a preferred coordinate frame changes; however, the observed periodicity cannot be interpreted as conclusive support for such a hypothesis.