Are we making earthquakes worse ?


Are dams at risk ?Last month the French magazine Science et Vie [Fr] dedicated a series of articles to the earthquake risks induced by dams, mines, oil drilling and geothermal power. You might think that these activities are without seismic risk.

But to their findings, around 200 earthquakes have been triggered by human activities so far. This can be explained by the billion of tonnes of coal, oil and minerals we have extracted so far.

This means that at least four energy sources – and two among the cleanest – are making earthquakes more frequent and more damaging.

Among the 200 earthquakes above mentioned, ten were above five of magnitude. Out of these ten, five were triggered by dams: Koyna, India in 1967 ; Srinagarind, Thailand in 1959 ; Hsinfengkiang in 1962 ; Kariba in Zambia in 1963 and finally Kremasta in Greece in 1966.

Art McGarr, a U.S. Geological Survey specialist stated in Science et Vie that there is a direct relation between the size of the activity and the magnitude of the earthquake.

Furthermore, researches carried out by Christian Klose, a geophysical hazards research scientist from Columbia University in New York, show that the Zipingpu dam reservoir may have triggered the Sichuan earthquake.

Wired Science published an interesting article that corroborates the findings of Science et Vie:

Some human actions can trigger much larger quakes along natural fault lines. That’s because humans, with the aid of our massive machines, can sling enough mass around to shift the pattern of stresses in the Earth’s crust.

Faults that might not have caused an earthquake for a million years can suddenly be pushed to failure, as Klose argues occurred during Australia’s only fatal earthquake in 1989. After the jump, we present the top five ways to create an earthquake.

Dams:

Water is heavier than air, so when the valley behind a dam is filled, the crust underneath the water experiences a massive change in stress load. For example, the Hoover Dam area experienced hundreds of quakes as Lake Mead filled. University of Alaska seismologist Larry Gedney explained, “Since [the dam] reached its peak of 475 feet in 1939, the level of seismicity has fluctuated in direct response to water level.

None of the shocks has been particularly damaging — the largest was about magnitude 5 — but the area had no record of being seismically active.” Other examples of dam-caused quakes abound and Klose’s research indicates that about one-third of human-caused earthquakes came from reservoir construction.

Mine a Lot of Coal:

Coal provides more than half the electricity in the United States and an even greater percentage in China. That means there are a lot of coal mines working overtime to pull the fossilized fuel out of the Earth. In total, miners pulled 6,195 million metric tons of coal out of the Earth in 2006 alone.

And coal mines often have to pump water out along with the coal, sometimes extracting dozens of times as much water as coal. Add it up and you have a huge change in the mass of a region, and huge mass changes refigure the earthquake stresses of an area, sometimes increasing the chance of an earthquake and other times lowering it. Klose’s work suggests that more than 50 percent of the human-triggered earthquakes recorded came from mining operations.

Drill a Gusher Dry:

Three of the largest human-caused quakes occurred near a natural-gas field in Uzbekistan, the Gazli. The combination of liquid extraction and injection changed the tectonic action in the field. The biggest of the trio registered as a 7.3. According to a major analysis by Russian scientists, “Few will deny that there is a relationship between hydrocarbon recovery and seismic activity, but exactly how strong a relationship exists has yet to be determined.” They caution that in regions where tectonic activity is already high, extracting oil and natural gas could trigger strong quakes.

Science et Vie - Avril 2009To conclude, f you read French I strongly recommend you to read the April 2009 issue of Science et Vie as it brings 15 pages of data and findings.

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