Coined by astrologer Richard Nolle, a supermoon is a nearly new or full moon that reaches the closest 10% of its Earth-Moon distance range during perigee (the closest point to Earth throughout the Moon’s orbital cycle). This phenomenon occurs approximately 5 times a year. Nolle has long been the sole perpetrator of the “supermoon effect” theory, arguing that the Earth is particularly subject to the Moon’s gravitational effects around the time of a supermoon such that it may contribute to an increased incidence of natural disasters within +/- 3 days of the supermoon…until the disaster in Japan struck.
Since the earthquake and tsunami disaster in Japan on March 11, 2011, there has been much discussion throughout the interwebs as to whether the earthquake was influenced by the March 19 extreme supermoon (particularly close supermoons) which occurred 8 days later. You may notice that this disaster did not strike within Nolle’s window of +/- 3 days, but that did not stop his followers from claiming that the supermoon had a part to play in the earthquake. This is an example of moving the goalposts by changing the criteria so that that this disaster still fits into the “supermoon effect” window. Such an act is unjustified as it contradicts the argued mechanism by which the “supermoon effect” is said to work – that the Moon’s gravitational effect is nearing its maximum. As Phil Plait noted, on March 11, 2011, the Moon was far from perigee at approximately 400,000 km (240,000 mi) away from Earth, which is further than average throughout the lunar orbital cycle.
Nolle and his reporters frequently report examples of disasters that have struck within days to weeks of supermoons. These arguments are merely anomaly hunting, as they report the “hits” and ignore the (many) misses. In order to make conclusions about the effect of supermoons on earthquakes we need to look at the whole spectrum of evidence, not just that which suits our agenda.
I took the liberty of looking at the records of the dates of every supermoon and every earthquake of 8.0 magnitude or greater since 1900. If supermoons have a real, measurable effect on the incidence of earthquakes, we can expect that they would have occurred with greater frequency around the time of supermoons than we would expect by chance. I have divided my calculations into 3 separate criteria: the +/- 3 days window prescribed by Nolle, and for the goalpost movers - +/- 1 week and +/- 2 weeks from the occurrence of a supermoon.
Within +/- 3 days of a supermoon:
There are on average 5 supermoons a year. A criteria of +/- 3 days gives a 7 day window, meaning that there would be approximately 35 days in the year that the Earth is particularly susceptible to the forces of supermoons. This equates to 10% of the year. It follows that if earthquakes occur at random intervals, they would have a probability of occurring by chance within the supermoon effect window 10% of the time.
Between 1900 and today there have been 87 earthquakes with magnitudes of 8.0 or greater. If supermoons have a real, measurable effect, we should expect more than 10% of these earthquakes to have fallen within +/- 3 days of a supermoon. Since 1900, 6 earthquakes of this magnitude have fallen within this window, which is just under 7% of all such earthquakes, and less than would be expected by pure chance.
Within +/- 1 week of a supermoon:
Approximately 75 days of the year lie within 7 days of a supermoon. This is 21% of the year. If supermoons have a real, measurable effect on earthquakes of magnitude 8.0 or greater we would expect more than 21% of them to have occurred within 7 days of a supermoon. Since 1900, 13 out of 87 earthquakes of this magnitude, or 15% have fallen within 7 days of a supermoon, which is less than we would expect by pure chance.
Within +/- 2 weeks of a supermoon:
Approximately 145 days of the year lie within 14 days of a supermoon. This is 40% of the year. If supermoons have a real, measurable effect on earthquakes of magnitude 8.0 or greater we would expect more than 40% of them to have occurred within 14 days of a supermoon. Since 1900, 31 out of 87 earthquakes of this magnitude, or 36% have fallen within 14 days of a supermoon, which is less than we would expect by pure chance.
What about the elusive EXTREME supermoon?
No earthquakes of magnitude 8.0 or greater have ever occurred within 3 or 7 days of an extreme supermoon. 1 earthquake of this magnitude (the disaster in Japan) has ever occurred within 14 days or less. Using this 1 incidence of a large-scale earthquake occurring within 8 days (not the +/-3 days that Nolle prescribed), and ignoring every single other extreme supermoon on record that did not cause a large-scale earthquake is nothing but anomaly hunting or searching for “the exception that proves the rule”.
So when we look at the whole spectrum of data on supermoons and earthquakes over the last 110 years rather than only noting those earthquakes that occurred near supermoons, we can see that earthquakes of magnitude 8.0 or greater do not occur with a greater frequency within 3 days (as prescribed by Nolle), 1 week, or 2 weeks of a supermoon. Consequently, there is no evidence to support the argument that supermoons have any effect on large-scale earthquakes.