Earthquakes becoming more common, scientists admit

By Ai Lung Nguyen - April 2010.

ENVIRONMENT - The number of earthquakes in recent years has been going up. The most recent was today's 6.9 magnitude earthquake in China which has killed over 400 people, but there is a lot of scientific debate about what has caused the recent increase.

If you've been keeping track of the earthquakes in China, Haiti, Chile and even huge tsunami/earthquake from 2004 you might start to wonder if earthquakes are becoming more common. There has also been an increase in tremors in the United States, Mexico and Japan.

This is actually true says seismologists, earthquakes in recent years have become more prevalent, but the cause is still being debated. Below is several different theories being tossed around by noted seismotologists.

#1. The recent seismic activity may simply be a temporary jump in earthquakes due to a variation in the Earth's lithosphere (The lithosphere is the outer solid part of the Earth.), but still within the acceptable range.

"Relative to the 20-year period from the mid-1970's to the mid 1990's, the Earth has been more active over the past 15 or so years," said Stephen S. Gao, a geophysicist at Missouri University of Science & Technology. "We still do not know the reason for this yet. Could simply be the natural temporal variation of the stress field in the Earth's lithosphere."

#2. Its just a coincidence that all these quakes happened in a short time period.

"From our human perspective with our relatively short and incomplete memories and better and better communications around the world, we hear about more earthquakes and it seems like they are more frequent," says J. Ramón Arrowsmith, a geologist at Arizona State University. "But this is probably not any indication of a global change in earthquake rate of significance."

#3. Melting polar ice caps caused by climate change has shifted the weight of ice on the polar regions of Earth's lithosphere. This causes the pressure in polar regions to buckle upwards while regions around the equator experience a downward effect.

#4. Overpopulation in seismically active regions.

As the human population skyrockets and we move into more hazardous regions, we're going to hear more about the events that do occur, says J. Ramón Arrowsmith. When large earthquakes strike in populated regions, news travels faster, especially with cellphones.

"What happens is when a lot of people get killed there's a lot of reporting of it, and if an equally big event occurs somewhere out in the middle of nowhere it doesn’t attract the attention," said G. Randy Keller, professor of geophysics at the University of Oklahoma.

"The [8.8-magnitude] earthquake down in Chile, that's an unusual event, those don't happen too often," Keller says. Seismologists would expect such an event at some point. "It sounds cold-blooded but it's an earthquake that occurred in a place that you'd expect it to sooner or later."

#5. Its normal for earthquakes to happen around the Ring of Fire (the Pacific Ocean). Over 90% of the world's earthquakes are felt in this region. The next most popular location is the Mediterranean Alpide belt (6%).

#6. Its a natural cycle to have quiet periods and busy periods when it comes to earthquakes. We could be entering a busy period. Usually busy periods are also accompanied by either an ice age or an extremely warm period.

"If you look at it globally the occurrence of earthquakes is confined to zones we already know have earthquakes but it's a largely random process and so sometimes it's a little quieter than normal and sometimes it's a little more active than normal. But it doesn't mean anything, because on a global basis these things aren't connected," says Keller.

"We're having a few more than the average, but nothing particularly remarkable. This was a magnitude 6.9 earthquake so on the bigger scheme of things it's not that big." If we get some really BIG earthquakes then we can have cause to worry.

So can we expect more in the near future? Yes, say scientists, although you have better odds of winning the lottery than predicting a big earthquake.