Bruce Bills, a geophysicist at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., and co-author of the new study published in the Journal of Geophysical Research. “Moonquakes reoccur again and again in the same locations at the same time of the month, which seems to link them to the monthly tidal cycles” he says, “but so far, nobody has been able to construct a physical model or clear pattern to explain the relationship.”