On November 6th Nigel Antony Gray predicted on his Facebook feed:

“Heads Up: On 14th November and a couple of days either side of that date, watch for a major earthquake, and quite possible in South Pacific area.”

On November 13th there was a magnitude 7.5 Earthquake on the south island of New Zealand. So far the death toll is two people. This was a significant quake along a known fault line that runs through the south island.

The internet was apparently very impressed with this prediction. Gray has long argued that earthquakes can be predicted by looking at the lunar cycle, because of the tidal forces of the moon on the earth. He is particularly fond of supermoons – when the moon is at perigee, the closest point in its orbit around the earth.

Supermoon

Tonight will be the most super supermoon since 1948. Last night and tonight the full moon will appear slightly larger than you are used to. You will not notice this difference, however. If you saw pictures of the apparent size of the moon side by side you can see the slight difference, but you would never notice it just by viewing the moon.

Also, the closer the moon is to the Earth the stronger the tidal forces of the moon. But again, there is a slight difference in tidal forces from the moon at close approach (perigee) and its most distant point (apogee).

Still, take a look, the moon is beautiful. If you have never done so, look at the moon with a pair of binoculars, or a telescope if you have access to one. Even with modest binoculars, you can see amazing detail on the surface of the moon. It becomes an actual world. Do it.

Tides and Earthquakes

Earthquakes are notoriously difficult to predict. They are inherently unpredictable. Strain forces build up along a fault line over long periods of time. Suddenly those forces give way and result in the fault like slipping slightly to reduce the pressure. There is no way to predict when that will happen with any accuracy.

What scientists can say is that the forces building up in a fault line are increasing and reaching a critical point, meaning that it is close to generating an earthquake. That is like saying, there are going to be hurricanes around North America this summer. We can only make general predictions, not specific ones.

People, however, do not like the unpredictable. Earthquakes can be devastating, and it would be of great practical value to be able to predict them precisely. This has spawned many theories about how to predict earthquakes.

One theory that has been looked at for over a century is the possible association of earthquakes and the phase of the moon, or other cycles of the moon such as apogee and perigee. Essentially, do the tidal forces produced by the moon (or the sun, for that matter) trigger earthquakes?

This is not a crazy idea. Tidal forces affect the land as well as the oceans. Solid land moves much less than the oceans – the maximal vertical displacement from the moon is 384 mm. This is small but measurable. This heaving could add a little extra strain to an already strained fault line, perhaps triggering a quake.

But, it just turns out that there is no significant effect here. A century of looking has failed to turn up any significant correlation between the tidal forces from the moon and earthquakes. GNS Science seismologist Dr John Ristau said of a recent Japanese study that found a tiny correlation:

“But basically what they found is that if you have a fault that is really close to the tipping point, a fault that’s almost about to break, that given enough time – probably a very short amount of time – would rupture in a major earthquake anyway, it just might happen because the tides can put some stress on the crust.”

This is hardly useful. If the quake is about to happen anyway, tidal forces may be the final straw that pushes it over. The bottom line is that this effect is so small it adds little to our predictive capabilities when it comes to earthquakes.

None of this has stopped Gray from claiming the exact opposite, that the moon, and specifically supermoon events, can be used to predict earthquakes.

Prediction vs Prophesy

The ultimate test of any scientific hypothesis is how well it makes predictions about future data. Scientific methods involve making and testing specific predictions systematically. The reason for this is because of the natural human tendency for confirmation bias – we will pick out those predictions that seem to come true, or just the data that supports our hypothesis.

Alleged psychics and prophets depend on this. One strategy they use is to make vague predictions that seem specific, but actually capture many possible outcomes. They could be vague about the time frame, the location, or the specifics of the event itself.

Another strategy is to predict high frequency events. If you do not live in an earthquake prone region, you may never or rarely experience earthquakes, making it seem like they are rare events. However, there are several million earthquakes around the globe every year. There are about 1,500 earthquakes a year that are between magnitude 5.0-7.9, and about one per year of 8.0 or greater.

Therefore, predicting that a strong earthquake will happen somewhere sometime is a sure bet. You can make the prediction sound more specific by giving yourself a finite window of time and specifying a region of the world, but even then your prediction may be highly likely to come true.

Gray essentially gave himself a 5 day window and the entire South Pacific as a region. Our naive sense of how likely this is to come true is deceptive. It is actually quite likely over any random 5 day period given the entire South Pacific.

Another strategy of alleged psychics is to make many predictions, then tout the ones that happened to come true. Also, there are many self-proclaimed psychics making predictions, and by chance alone some of them are going to get lucky.

Taking all of this into account, the fact that someone said there may be an earthquake in the South Pacific during that week is not at all impressive. Pretty much after every major earthquake someone comes forward to take credit for predicting it.

Only by looking at data systematically can we determine if there is any real effect. Scientists have been doing this earnestly for a century with regard to tidal forces and earthquakes, and there simply is only a tiny effect at best, not enough to make worthwhile predictions.