Are there more earthquakes than there used to be?

Previously published Slate articles made new.
April 16 2010 10:40 AM

Are There More Earthquakes Than There Used to Be?

How human activity affects the tectonic plates.

The 2010 Chinese earthquake.
Epicenter of the recent China earthquake

An earthquake with a magnitude of 7.1 struck China on Tuesday, and local monks say the death toll could reach 10,000. On Thursday, a much smaller quake hit Utah. And in February, a huge earthquake in Chile damaged 500,000 homes. The month before that, Brian Palmer set out to explain whether the disaster in Haiti had anything to do with all the other earthquakes being reported around the world. That column is reprinted below.

A 7.0-magnitude earthquake struck Haiti on Tuesday, three days after a 6.5-magnitude quake rocked the extreme north of California. In total, there have been 270 earthquakes worldwide in the last week. Can humans affect the frequency of earthquakes, just like we've affected the global climate?

Advertisement

Not significantly. While certain activities, like mining, oil extraction, and dam-building can trigger an earthquake by changing the weight on tectonic plates or lubricating the joints between them, there is no evidence that humans have caused a quake of greater than 5.3 in magnitude. Major earthquakes like the one in Haiti are natural and unstoppable events. If Earth's plates are going to shift and cause one of these disasters, there is nothing we can do.

The frequency of major earthquakes has remained fairly constant throughout recorded history. Since 1900, there have been approximately 18 earthquakes of 7.0 or greater magnitude per year. (One usually crosses the 8.0 barrier.) There are no data suggesting an upward trend in that rate. Seismologists are detecting more and more smaller quakes, but that phenomenon can be attributed to the quality and quantity of detection devices: Since 1931, the number of seismological stations worldwide has increased from 350 to more than 8,000.

Because earthquakes occur deep beneath Earth's surface, most of the human activity capable of causing earthquakes involves digging or drilling. For example, oil companies sometimes inject water into their wells to force out the black gold under pressure. The water, pumped to a depth of thousands of feet, can decrease the friction holding two plates in place, causing a slip and a minor tremor.

The largest earthquake known to be triggered by people occurred four decades ago in Colorado. In 1962, the U.S. Army drilled a 12,000-foot-deep well to dispose of the waste from a chemical and conventional weapons factory in Commerce City. Over four years, the reservoir was filled with 165 million gallons of contaminated liquids. The Army stopped pumping when it realized that the process had caused a series of small-to-moderate tremors. One year later, a 5.3-magnitude quake caused more than $1 million in damage to the Denver metropolitan area.

As water accumulated behind Hoover Dam in the late 1930s, hundreds of small earthquakes shook the area. Some suspect that the 7.5-magnitude Koyna earthquake in India in 1967 was caused by a nearby reservoir, but most seismologists reject this theory. Many scientists now fear that the Three Gorges Dam in China poses a serious seismic risk. If the dam causes an earthquake that fractures the retaining wall, flooding would likely affect the millions of people living downstream.

Nuclear detonations are extremely unlikely to cause major earthquakes, contrary to Hollywood depictions, but subterranean tests can register small amounts of seismic activity. A 1968 nuclear test with the code name "Faultless" did manage to open up a new fault in the Nevada desert. The incident moved seismographic needles, but that was mostly attributable to the nuclear explosion itself rather than to any resulting tectonic activity.

Got a question about today's news? Ask the Explainer.

Become a fan of Slateand the Explaineron Facebook. Follow us on Twitter.

Brian Palmer writes about science, medicine, and the environment for Slate and the Natural Resources Defense Council. Email him at explainerbrian@gmail.com. Follow him on Twitter.

TODAY IN SLATE

Culturebox

The End of Pregnancy

And the inevitable rise of the artificial womb.

Doctor Tests Positive for Ebola in New York City

How a Company You’ve Never Heard of Took Control of the Entire Porn Industry

The Hot New Strategy for Desperate Democrats

Blame China for everything.

The Questions That Michael Brown’s Autopsies Can’t Answer

Foreigners

Kiev Used to Be an Easygoing Place

Now it’s descending into madness.

Technology

Don’t Just Sit There

How to be more productive during your commute.

There Has Never Been a Comic Book Character Like John Constantine

Which Came First, the Word Chicken or the Word Egg?

  News & Politics
The Slate Quiz
Oct. 24 2014 12:10 AM Play the Slate News Quiz With Jeopardy! superchampion Ken Jennings.
  Business
Moneybox
Oct. 23 2014 5:53 PM Amazon Investors Suddenly Bearish on Losing Money
  Life
Outward
Oct. 23 2014 5:08 PM Why Is an Obscure 1968 Documentary in the Opening Credits of Transparent?
  Double X
The XX Factor
Oct. 23 2014 11:33 AM Watch Little Princesses Curse for the Feminist Cause
  Slate Plus
Working
Oct. 23 2014 11:28 AM Slate’s Working Podcast: Episode 2 Transcript Read what David Plotz asked Dr. Meri Kolbrener about her workday.
  Arts
Brow Beat
Oct. 23 2014 6:55 PM A Goodfellas Actor Sued The Simpsons for Stealing His Likeness. Does He Have a Case?
  Technology
Technology
Oct. 23 2014 11:47 PM Don’t Just Sit There How to be more productive during your commute.
  Health & Science
Science
Oct. 23 2014 5:42 PM Seriously, Evolution: WTF? Why I love the most awkward, absurd, hacked-together species.
  Sports
Sports Nut
Oct. 20 2014 5:09 PM Keepaway, on Three. Ready—Break! On his record-breaking touchdown pass, Peyton Manning couldn’t even leave the celebration to chance.