The name SuperMoon was coined by astrologer*
Richard Nolle in 1979, defined as:
...a new or full moon which occurs with the Moon at or near (within 90% of) its closest approach to Earth in a given orbit (perigee). In short, Earth, Moon and Sun are all in a line, with Moon in its nearest approach to Earth.
The term supermoon is not widely accepted or used within the astronomy or scientific community, who prefer the term perigee-syzygy. Perigee is the point at which the Moon is closest in its orbit to the Earth, and syzygy is a full or new moon, when the Earth, the Moon and the Sun are aligned. Hence, a supermoon can be regarded as a combination of the two, although they do not perfectly coincide each time. Syzygy may occur within a maximum of 12 hours from perigee during a supermoon, and 1 hour from perigee during an extreme supermoon.
(* Please note astrologer - not astronomer. One earns a living flogging horoscopes to the gullible and the other is a scientist.)Speculative link to natural disasters
Richard Nolle has argued that within ±3 days of a supermoon, the Earth is more subject to natural disasters such as earthquakes and volcanic activity due to the Moon's increased gravitational force. Speculations have moved the goalposts to within 1 or 2 weeks of a supermoon to suggest a causal relationship with specific natural disasters such as the 2011 Tōhoku earthquake and tsunami and the 2004 Indian Ocean earthquake and tsunami. Such a widening of the effect window is unjustified as in both cases the Moon was farther from the Earth than average, making a supermoon effect impossible.
Some studies have reported a weak correlation between lunar activity and shallow, very low intensity earthquakes. However, no evidence has been found of any correlation with major earthquakes. Unjustified claims that the lunar tides trigger earthquakes are rooted in a lack of appreciation that the stress in the Earth is described by a tensor with six independent parameters and that earthquakes occur as slip on existing, weak fault planes. Any change in stress, by lunar tides, by impounding a reservoir, or by a large nearby earthquake, changes the local stress tensor in specific directions. If one wishes to estimate whether a given change advances or hinders slip on a fault, one has to know the orientation of the fault. It is equally likely that the change of the stress due to the moon clamps the fault shut, rather than advancing slip on it. This is why Ohtake has carefully considered the orientation of the fault planes in earthquakes that he showed were correlated with lunar tides.
The 2011 Tōhoku earthquake and tsunami is the only earthquake of 8.0 magnitude or greater to have occurred within 2 weeks of the 14 extreme supermoons from 1900 to the present date, suggesting that the claim of a supermoon effect on the incidence of large-scale earthquakes is unjustified.http://en.wikipedia.org/wiki/Supermoon
As i have said before and will say it again. Only the gullible would take this numpty seriously.