What Do All the Recent Earthquakes Mean?

In the past couple of days, the earth has seen a number of large earthquakes on different sides of the world.

The coast of Sumatra was shaken by an 8.6 temblor, followed by an 8.2 aftershock last night, the United States Geological Survey reports. Hours later, Mexico was hit by a 6.5 quake, followed by a 6.9. Then, there was a 5.9 off Oregon's coast, followed by a 5.3 in California.

The numbers may look scary, but analysts at the USGS say this isn't necessarily anything to worry about - it doesn't mean the "big one" is about to hit, and it doesn't affect the likelihood of a massive quake hitting anywhere.

There are approximately 20,000 earthquakes every year, or about 55 per day. The vast majority of these quakes are small, and we can expect about 16 major earthquakes in any given year, according to the USGS. There are about one or two earthquakes in the 7.0 - 8.0 range each month (the last one in that range happened in Chile on March 25).

Earthquakes are, by nature, random occurrences. Nobody can predict when one will happen, or how big the next one will be, the USGS says. Because they happen randomly, there can be clusters of quakes, usually in the form of a mainshock and its aftershocks. However, it is unlikely that yesterday's 8.6 quake off the coast of Sumatra caused or affected the later earthquakes in Mexico and the U.S. West Coast, Lucile Jones, Science Advisor for Risk Reduction at the USGS told ABC News.

"These have all been far enough apart that they fall within the random category. It only seems significant because it is human nature to look for clusters and explanations," Jones explained. "We see patterns, like constellations in randomly placed stars, but it doesn't necessarily mean that there is any connection."

According to USGS measurements, five of the biggest earthquakes since 1900 happened in the last ten years, including the 8.6 temblor yesterday. This also isn't anything to worry about, Jones said.

"Last year, after the massive quake in Japan, scientists did an analysis looking for some sort of statistical significance to the size and location of the quakes in the region, and found that there was none," Jones told ABC. "Would one more quake change that analysis? Maybe, but probably not. It's human nature, not science, that makes us think 'the big one' is imminent. We have just as much chance of it hitting today as we did two days ago."

The USGS also notes that "improvements in communications and the increased interest in natural disasters, the public now learns about earthquakes more quickly than ever before."

What's more interesting for scientists, Jones said, is the type of quake yesterday's 8.6 temblor was. The biggest quakes - like the 9.0 that caused devastating damage in Japan last year - occur when one tectonic plate moves underneath another. Yesterday's earthquake was a strike-slip quake, which happens when two plates slide horizontally past each other.

"Until yesterday, we didn't think a strike-slip quake could possibly reach the magnitude of 8.6," Jones said. "That was wrong - apparently it can, and that's something we'll really have to study."

The implications of this development could be serious. The San Andreas fault, which runs through California, is a strike-slip fault. It was previously thought that a big quake along that fault wouldn't get into the 8.5 or higher range, but in light of yesterday's quake in the Indian Ocean, that thinking might have to change.

Because earthquakes are random and unpredictable, it's important to take steps to remain safe just in case, Jones said.

"You can't control earthquakes, but you can control your environment," Jones said. "Make sure your home is earthquake ready, store water, make plans. You may not know when an earthquake will happen, but you can make sure you're safe when it does."