EARTHQUAKES
Over in the United States, two scientists from respected universities have come up with a theory that suggests a big increase in devastating earthquakes in 2018 following a tiny slowing in the Earth’s rotation.
‘‘The correlation between Earth’s rotation and earthquake activity is strong and suggests there is going to be an increase in numbers of intense earthquakes next year (2018),’’ Roger Bilham of the University of Colorado told The Observer.
Bilham and Rebecca Bendick of the University of Montana presented a paper on the link between seismic activity and the Earth’s rotation speed at the annual meeting of the Geological Society of America. The slowdown in Earth’s rotation is tiny – a millisecond a day sometimes – which can be measured by atomic clocks.
Bilham and Bendick found that periods when the number of intense earthquakes had increased followed periods of about five years when the Earth’s rotation slowed slightly. Our planet began one of its periodic slowdowns around four years ago.
In November, Bilham said: ‘‘Next year we should see a significant increase in numbers of severe earthquakes. We have had it easy this year. So far we have only had about six severe earthquakes. We could easily have 20 a year starting in 2018.’’
The link between the Earth’s rotation and the number of big earthquakes was unclear, but slight changes in the behaviour of the Earth’s core could be causing both effects.
Bilham and Bendick looked at earthquakes of magnitude 7 and greater since 1900, finding five periods when the number of big quakes increased significantly. In those periods there were 25-30 intense quakes a year, compared to an average of about 15 at other times.
However, Associate Professor of Geology at Auckland University Phil Shane challenges the theory. He doesn’t believe there’s any evidence to support the proposition that the slowing down of the earth’s rotation has any impact on earthquakes.
‘‘Yes, the Earth does slow down gradually. Two hundred to four hundred million years ago a day was only 22 hours long, but today it’s 24 hours due to the rate of change in milliseconds over time.
‘‘I believe it’s just speculation at this point and you shouldn’t be concerned.’’
This appears to be reflected in a follow-up report by The Washington Post in which Bendick told the newspaper that she does not want the public to panic.
She emphasised there was no foolproof way to predict an individual earthquake.
Earthquakes occur when potential energy stored along cracks in the planet’s crust is released, sending seismic waves through the Earth. Since scientists know where those cracks exist, and how they are likely to convulse, they can develop forecasts of the general threat for an area.
But the forces that contribute to this energy buildup and trigger its release are global and complex, and scientists still cannot sort out exactly how it might unfold.
Historically, the field of earthquake forecasting has seen some particularly outlandish claims. People have tried to predict temblors based on the behaviour of animals, gas emissions from rocks, low-frequency electric signals rippling through the Earth – all without much success.
For that reason, Bendick says, ‘‘it’s a little bit scary to get into the game.’’ But getting a prediction right can mean the difference between life and death. The stakes are too high not to try.
Initially, the data she and Bilham analysed appeared random. But then they added a new number to their analysis: the ‘‘renewal interval,’’ or the amount of time a given earthquake zone requires to build up potential energy for a really big quake.
‘‘Basically you can think of earthquakes as something like a battery or a neuron; they have a certain amount of time they need to be charged up,’’ Bendick says.
Bendick and Bilham hope the pattern might help scientists and public officials make some sense of the Earth’s unpredictable shaking. If disaster planners can say with some assurance that the planet is entering a period in which quakes are more likely, they might have an easier time making the case for preparedness measures.
But that doesn’t necessarily mean 2018 will be a particularly devastating year. For one thing, the kinds of temblors Bendick and Bilham analysed happen in areas that are already earthquake-prone — Japan, New Zealand, the West Coast of the United States. For people who live in those regions, there is always a risk of a quake, and it is always good to be prepared.
Their study is about probabilities, not predictions, Bendick cautioned. Earth’s slowing doesn’t mean that a quake will happen in the next year or so, just that the likelihood may have gone up.
In New Zealand, GeoNet’s earthquake forecast for the Canterbury region has predicted a less than one per cent chance of an earthquake of higher than a seven on the Richter scale occurring in the next year. This is compared to their forecast that there is a six per chance of a similar size earthquake occurring in Kaikoura for the same period while there is a 53 per cent chance of an earthquake of between six and 6.9 on the Richter scale.