Earthquake in Mexico

The Year of the Earthquake? Not Quite. Despite High-Profile Events, Quakes Are Not Increasing (Populations Are).
Molly O'Toole

People stand near the ruins of collapsed houses after a quake in Yushu County, northwest China's Qinghai Province. Xinhua/Landov.
Yesterday, a 6.9-magnitude quake struck Qinghai, China, resulting in an estimated 400 dead and 10,000 injured. One week before that, a 7.7 tremor hit Northern Sumatra, Indonesia. Two days before that, a 7.2 shook Baja, Mexico. At the end of February, Chile shuddered under an 8.8 earthquake, little over a month after a 7.0 crumbled Haiti and killed nearly 230,000. With such a list, 2010 appears to be the year of the apocalypse or, at the very least, unnaturally active for these natural disasters.

Not according to the United States Geological Society and other experts. They say we’re not getting more quakes than usual, we’re just paying more attention. Even earthquakes of magnitude 7.0 or greater have remained fairly constant throughout history: based on records since about 1900, approximately 17 major earthquakes, ranging from 7.0 to 7.9, and one “great” earthquake—at 8.0 magnitude or above—are expected in any given year. Not that such statistics should be taken lightly; even a slight shift of 1.0 magnitude higher on the seismic scale creates 10 times more ground motion and releases about 32 times more energy—the best indicator of the destructive power of an earthquake. So far for 2010, the 8.8 giant in Chile places into the “great” category, and five major tremors of a 7.0 magnitude or more have been recorded.

“This year has been remarkable in the number of earthquakes in close succession that have had human impacts,” says Michael Blanpied, USGS's associate coordinator for earthquake hazards. “But the number of earthquakes, from the earth’s perspective, is not unusual … it’s exciting and it’s terrible, but it’s not unusual.”

Blanpied notes that in any given year the number of earthquakes varies, with many years falling outside the range. In the last 12 months there have been a normal 18 earthquakes at 7.0 and above, while over the course of the last three and a half months there have been six—only slightly above average for that time period.

In the past decade, 2007 actually saw the largest earthquakes, with four of 8.0 magnitude or larger. Though 2009 only witnessed one such “great” quake, last year 16 tremors of 7.0 or higher shook the world. And 2004 was the deadliest year, with 228,802 estimated deaths from earthquakes (though as of yesterday, 2010 has already seen approximately 223,142). Yet, according to Blanpied, 1943 had 32 earthquakes at 7.0 or above—twice the annual average—and one of the largest quakes ever recorded, a 9.5 magnitude, struck Chile in 1963.

The best explanation is not a global growth in the frequency or power of earthquakes, but rather a number of factors contributing to that perception, namely an increase in the number of earthquakes that seismic centers are now able to locate. According to the USGS, in 1931 there were only roughly 350 seismograph stations in the world; today there are more than 8,000. Currently, the National Earthquake Information Center locates roughly 50 earthquakes a day and 20,000 annually. Drastic improvements in communications technology now allows these stations to fire data around the globe, detecting and describing quakes that would have previously gone uncharted and informing the public in a broader way than ever before—even, according to USGS spokeswoman Clarice Ransom, through Twitter.

“Seismic networks have become more and more modern,” says Blanpied, “and can report an earthquake with even greater speed and accuracy—within a few minutes anywhere in the country, and within a few minutes anywhere in the globe, from the vulnerability of structures to how many people were shaken.”

Another factor is location. Had these recent earthquakes occurred deep in the ocean, not near dense population, they would not be given the same attention.

“Probably the more sobering [factor], frankly, is there are more and more of us,” Blanpied says. “The biggest areas of population growth on the planet are those near the equator, and a lot of the seismic hazard of the earth is in that area … The earth is chucking earthquake darts at us all over the planet, and we’ve put out more and more targets. There’s more and more chance of an earthquake hitting a target, and every once in a while it hits a Haiti, a bull’s-eye.”

As for the seeming connection between this year’s tragic quakes, Blanpied says not enough is yet known about the nature of earthquakes to establish concrete ties between seismic events—though for quakes such as those in Haiti and China, whose effects were relatively localized and the distance between them great, any connection in highly unlikely.

“Chile was the fifth biggest earthquake in a century,” says Blanpied. “Those seismic waves rang around the world. It is possible those had influence on other faults that were ready to have earthquakes. Perhaps we will learn over time that major earthquakes have effects on those elsewhere, but at least not for sometime in the future … certainly not at the level of knowledge that would allow us to take any kind of action, but, hopefully, they can serve as reminders.”