EARTH tides with stress gradients exceeding 10−8 bar/m (ref. 1) and with predominant periods at approximately 12 h, 24 h and 14.7 day constitute the largest short period oscillatory stress in the Earth's crust2. The release of secular tectonic strain accumulation in the crust by tidal triggering has been suggested3–5, and many attempts2,3,5–8 have been made to correlate earthquake times with records of Earth tides. All these attempts have proved unable conclusively to relate tides to the occurrence of earthquakes, although microearthquakes may prove to be an exception9.