Tidal triggering of earthquakes is the idea that tidal forces may induce seismicity. In connection with earthquakes, syzygy refers to the idea that the combined tidal effects of the sun and moon – either directly as earth tides in the crust itself, or indirectly by hydrostatic loading due to ocean tides – should be able to trigger earthquakes in rock that is already stressed to the point of fracturing, and therefore more earthquakes should occur at times of maximal tidal stress, such as at the new and full moons. Indeed, recent work has concluded that "large earthquakes are more probable during periods of high tidal stress".