Losing the Plot: Can Explosions Trigger Earthquakes?

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What price the mad scientist? (Image from US Government)

What price the mad scientist? Image credit: U.S. Department of Energy

It’s a popular plot device in disaster movies. Cinema audiences sit munching their popcorn, while the villain plants a bomb (preferably nuclear) somewhere in California and holds the world to ransom with his (or her) threat to generate a mega-earthquake and destroy the world. But if you’ve ever woken in the night in a cold sweat worrying that such a thing might come true, relax. The myth of the bomb that causes a SuperQuake can be well and truly… exploded.

Holding the World for Ransom: Why it Won’t Happen

The idea may be a good one, and it may make for a great movie – but scientists are unequivocal in asserting that such a thing just can’t happen. In the words of the United States Geological Survey: ‘It’s just not physically possible’ – and the organisation’s George Choy told Decoded Science exactly why.

For a start, the villain would need to know where and when an earthquake was likely to happen. And while seismologists are able, up to a point, to predict when an earthquake will occur, there is enormous uncertainty – hundreds of kilometers in terms of distance, and years or even centuries in terms of time. So our villain would either need a so-far unheard of accuracy in terms of prediction, or he would need to be unbelievably lucky.

He would also need a mighty large bomb. Human-induced stresses on our planet are tiny compared to the natural effects caused by gravity within the solid earth, and even these have not been shown to have any positive correlation with earthquake activity. As George Choy points out:

“The  energy of an explosion does not come close to overriding forces that are constantly acting in the earth and which still do not obviously trigger large earthquakes.”

The scientific premise has, effectively, been tested already during the nuclear tests of the Cold War. The USGS reports that, in 1971, the largest thermonuclear device to be tested was detonated close to the highly seismically-active Aleutian Islands. Despite its size, (with a yield of 5 megatons, the blast was hundreds of times larger than the bomb which devastated Hiroshima) it failed to trigger any earthquakes.

Saving the World From an Earthquake: Why That Won’t Happen Either

So, what if it isn’t the villain, but the hero who wants to trigger an earthquake? Let us say that an earthquake of M8 is expected to strike Los Angeles (again supposing that there is sufficient knowledge to identify exactly where, if not when, the earthquake will occur). Would it be possible for our action hero to use explosions, conventional rather than nuclear, to create smaller earthquakes and so avert the coming of The Big One?

San Andreas Fault: not at risk from conventional or nuclear explosions (Image from USGS)

San Andreas Fault: not at risk from conventional or nuclear explosions (Image from USGS)

Earthquakes are generated by accumulated stress in the earth’s crust. Beyond a certain (variable) threshold, the stress is released by an eventual tremor, and that the theory is that by releasing a smaller earthquake – or rather, a series of earthquakes – it would be possible to reduce either the scale of the expected event or its magnitude. So, how practical is the save-the-Earth-with-explosions scenario?

Decoded Science asked Dr. Roger Musson, of the British Geological Survey. According to Dr. Musson, such a scenario is theoretically possible – but in reality the practicalities are just too problematic. Even assuming knowledge of where an when the tremor will strike, he points out that to release the stress which would accumulate for an M8 earthquake, our hero would have to co-ordinate the detonation of around 900 devices, each capable of generating an earthquake of M6.

To put that in some perspective, USGS statistics indicate that, annually worldwide, there is an average of only 134 earthquakes of between M6 and M6.9. And even then, the theory assumes both that the size of the earthquake can be controlled – which it can’t – and, crucially, that so many earthquakes of M6 (such events have killed hundreds or even thousands in the past) are considered worth the risk.

Explosions and Earthquakes: a Reality Check

So, we can sit back with our popcorn, and not worry too much about mad scientists interfering with the earth’s natural processes, right? Or can we? There is emerging evidence that the process of fracking (a technique used to recover natural gas from shale) may interfere in just such a way.

In northern England, commercial shale oil extraction has recently been suspended after being blamed for the occurrence of earth tremors in the UK. But even here, the scale has to be considered – the ‘quakes’ were M2.3 and M1.5 – and there are upwards of a million events of this magnitude occurring annually. So relax, sit back and enjoy the film. Oh, and pass me the popcorn…

Resources

BBC news online. Blackpool Shale Gas drilling suspended after quake. Accessed 31 October, 2011.
USGS. Can Nuclear Explosions Cause earthquakes? Earthquake facts and statistics.Accessed 31 October, 2011.

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© Copyright 2011 Jennifer Young, All rights Reserved. Written For: Decoded Science

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