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Matt Ridley is the author of provocative books on evolution, genetics and society. His books have sold over a million copies, been translated into thirty languages, and have won several awards.

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Seismic risks depend on location, not technology

A hydro dam created the largest man-made earthquake

The Times published the following article by me last week. I have inserted updates to clarify one issue.

On 1 June this year a Mr Andrew Noakes was having lunch in Shropshire when "I thought I heard something. The sound only went on for a few seconds and then it stopped. There was no shaking cutlery or furniture." It was a natural earthquake, bigger than the ones caused by fracking in Lancashire last year. Worldwide there are a million a year of a similar size. Very few are even noticed. A magnitude 2.3 tremor is to a dangerous earthquake as a tiny stream is to the Amazon: the same sort of thing but much less likely to drown you.

By contrast, an earthquake that was 180 million times more energetic killed 80,000 people in 2008 in Sichuan. We now know it was almost certainly man-made, or at least man-triggered. The Zipingpu reservoir, designed to generate hydro-electric power, had been filled with water shortly before the fault beneath it failed.

A report by Fan Xiao, chief engineer of the Regional Geological Survey Team of the Sichuan Geology and Mineral Bureau, analysed 60 studies of the event and concluded that "the mounting body of evidence and analysis indicates that the magnitude 8 earthquake was triggered by the mass loading and increased pore pressure caused by the Zipingpu reservoir".

Admittedly the study was translated and published by Probe International, a Canadian pressure group that campaigns against large dams and is funded partly by the nuclear industry, but others have reached the same conclusion. Professor Christian Klose of Think Geohazards in New York has concluded that the 300m tonnes of water in the Zipingpu reservoir effectively "advanced the clock" on a fault that would not have failed for another 60 years.

That dams cause earthquakes is not a new or far-fetched idea. Dr Klose has catalogued 92 man-made earthquakes, about half of which were caused by dams. One at Koyna in India is still occasionally causing the ground to shake decades after being filled. But think of the implications of this news. It would make the Sichuan earthquake the second largest man-made death toll in a single event, after Hiroshima, but bigger than Nagasaki and Dresden.

To put it unfashionably, the second biggest man-made disaster on record was caused by the search for renewable energy. Geothermal energy, too, can cause earthquakes. Two years ago the city of Basel called a halt to a project intended to extract heat from the rocks deep beneath the city after an earthquake was caused by the drilling. Basel was destroyed by an earthquake in 1356.

[Update: I am told that the company responsible for the Basel event began an intensive programme of hydraulic fracturing at depths up to 5km in contradiction to expert advice and on an active fault boundary. Basel is actually the site of Central Europe's largest ever earthquake in 1356 measuring 7.1 on Richter. The lesson is NOT that geothermal energy -- or dams or gas -- are inherently dangerous but that any of these activities in a seismically sensitive zone near a build-up area are unwise though quite safe elsewhere. Britain is a very very low risk place for big earthquakes. It's the location, not the technology that matters.]

Compared with dams and geothermal projects, the seismic risks of fracking, a procedure that has been used for 60 years to open the pores in rocks to release oil or gas, are not only very small, but extremely well tested. More than 100,000 frackings were carried out in the United States last year and none caused a tremor larger than the Blackpool one-which was in any case barely enough to cause a ripple on your coffee.

If it's earthquakes that worry you, campaign against dams, not gas.