Amazing Correlation
“The numbers of earthquakes that have occurred each year in the past century are well known. The changes in Earth’s rotation rate are also well known,” claimed Roger Bilham, who is currently a geophysicist from the University of Colorado Boulder, and who was the study’s co-author. “All we have done is to compare these two well-known lists of numbers and report an interesting and useful relationship.”
The general idea is that when the Earth spins slower, it causes the equator to shrink. But the problem is that the Earth’s tectonic plates are not capable of shrinking as easily as the equator, when means the plates’ edges get squeezed. Even though the amount of squeezing is not very significant, it actually puts more stress on those plates which already are under stress, and where earthquakes more likely to occur.
Historical pattern
Bilham and also his associate, Rebecca Bendick, who is also a geophysicist but comes from the University of Montana in Missoula, examined the past history of earthquakes that have a magnitude of 7 or more since 1900.
Since 1900, there have been roughly 15 major earthquakes annually on average. But during certain time periods there have been anywhere from 25 to 35 earthquakes with magnitudes greater than 7 occur annually. So when the researchers examined these periods more closely, they discovered these time periods correlated to those periods when the Earth was spinning slower, which means the days get a little longer. Modifications in the Earth’s rotational speed are often created by weather events like El Niño, sometimes caused by ocean currents, and even the currents of Earth’s molten core. When these fluids speed up, then the solid Earth has to slow down.
It is because NASA has been tracking the day’s length to each microsecond that these Earth spin slowdowns can actually be forecasted some 5 years in advance.
Based on this information, Earth is now entering a period of slower rotation that will be prolonged. And because of this, next year will most likely see more earthquakes, according to past data. Where the average year will experience around 15 earthquakes with a magnitude of 7 or more, the upcoming four years may something like 20 major earthquakes.
“Knowing that earthquakes will be more plentiful in five or six or seven years is useful because if a city planning department is considering retrofitting buildings to make them earthquake-safe now, or in 10 years’ time, the knowledge that more earthquakes are on their way may make them act now, rather than later,” Bilham stated.
However, this rotation effect will usually only impact the areas that have faults which are experience great stress already and at elevated risks of rupture.
“We have no information on where these earthquakes will occur, except that they will occur at the world’s plate boundaries,” Bilham noted.
Possible effect
“It’s a very interesting possible effect,” claims Amos Nur, who is a notable geophysicist from Stanford University in California, who did not take part in this research. “Even though the rotation rate changes so little, the size of the mass [of the Earth] and the inertia are so great, you don’t need a huge change in rotation to have a change in stress.”
Researchers still suffer from a poor understanding of the things that actually trigger an earthquake, and really don’t currently have any way to predict them. So he believes it is still quite impossible to definitively attribute any earthquake on the Earth’s rotation. But he still believes there are several ways to validate the results of this study.
“The next step would be to go back and try to model what happens to the stress inside the Earth,” when its rotation changes, Nur said. “It’s not ridiculous. It’s quite feasible.”
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