Study: Massive quakes do not trigger other big quakes
However, monstrous earthquakes like the one in Japan generate local aftershocks within a radius.
The study was published in the online edition of ‘Nature Geoscience.’ Dr. Tom Parsons was the leader of the study, and Aaron Velasco was the co author.
To collect enough proof for their theory, they looked at the earthquake records of around the world for the past 30 years, ending in 2009.
During this timeframe, there were 205 huge earthquakes with a magnitude of 7 or greater, and 25,222 moderate ones with magnitudes between 5 and 7.
They calculated the relative timing, to find out if one major earthquake triggered other earth shattering quakes.
Dr. Tom Parsons works at United States Geological Survey, and co-author Aaron Velasco is from University of Texas.
The aftershock effect
In their study, they explained how big earthquakes send aftershocks all over the world.
Parsons explained, "When you have a big earthquake like the [recent] one in Japan, it sends out seismic waves, some of which get trapped in the Earth's crust. These waves bounce around in the upper 20 or 30 kilometers and they travel at about 4 to 5 kilometers a second.
"At long distances away from the main shock, they are the highest amplitude waves seen on a seismogram, and they are primarily responsible for triggering other earthquakes. We looked at the seismic arrivals at different stations from a dozen large earthquakes and we saw all these little earthquakes that were associated with them."
Parsons added, "When we put it all together, we found that there were a surprisingly large number of earthquakes triggered all over the world in all kinds of places, including Australia. It became clear to us that the whole planet is basically an aftershock zone after big earthquakes."
The researchers discovered that there was a "significant increase" in seismic activity in neighboring areas of the disaster affected zone.
They did find an increase in moderate quakes, but only within 600 miles of the primary event, and nearly all within 375 miles. But beyond 600 miles, the number of moderate quakes after a big event was nothing abnormal.
No connection between massive earthquakes
This confirmed the belief that a big quake places stress on a nearby section of the same affected area, which then rips apart.
But, beyond this localized knock-on effect, which usually takes place two or three crack lengths farther down the same fault, there is no increase in seismic risk.
The study stated, "The regional hazard of larger earthquakes is increased after a main shock, but the global hazard is not.”
Parsons also said that to confirm his theory, he observed the world map of earthquakes after the recent Japan earthquake to find out any distant effect, but he found none.