© USGSA map of shaking intensity of the recent aftershock.
So far, 5,229 aftershocks have rattled the tectonic boundary that ruptured off the coast of Japan's Tohoku region in March 2011. The magnitude-9.0 earthquake was the fifth largest earthquake ever recorded.
The Sunday (May 20) quake is listed as both magnitude 6.0 and 6.4. If it proves to be the latter, it would be the largest aftershock since March 14, when a magnitude-6.9 earthquake hit the region.
Magnitude-6.0 quakes can cause serious damage if they hit near populated areas, yet the bulk of Japan's significant aftershocks have hit out at sea, many miles from land, and have caused relatively few problems.
This recent quake caused only light shaking for residents of northern Japan, according to U.S. Geological Survey (USGS) data. It occurred beneath the Pacific Ocean, about 60 miles (96 kilometers) east of Miyako, a coastal town devastated by the deadly tsunami that followed the March 2011 earthquake.
"With an earthquake this big, you can have aftershocks for months and years," said Paul Earle, a seismologist with the USGS. You can't say when or where they'll happen, he told OurAmazingPlanet, but they tend to decrease in number exponentially.
However, he added, there's an equal chance of getting a big aftershock or a small one. There tend to be fewer powerful aftershocks the more time goes by, but that's only because there are fewer aftershocks in general.
In total, 82 aftershocks of magnitude 6.0 or higher have hit since the Tohoku quake. The two largest, a 7.9 and a 7.7, hit on March 11, in the hours following the colossal main shock.
"Aftershocks are just earthquakes - they look exactly the same," said Don Blakeman, a geophysicist with the USGS. "The only thing that defines an aftershock is it's in the same basic location and has the same type of mechanism as the main shock," he told OurAmazingPlanet.
And aftershocks happen for the same reason a main shock happens, Earle said - when the stresses on either side of a fault exceed the friction that's holding it together.
In the case of Japan's Tohoku earthquake, the stresses that had built up were enormous. The aftershocks that have continued in its wake are the result of changes in the way stress is distributed around the fault.
"It's difficult to express how big this earthquake was compared to other earthquakes," Earle said. "When you have an earthquake this big, it totally reorients the stress that existed before it, and the Earth responds," he said.
The plate is still being pushed under by the pull of gravity and a slow methodical movement of the tilting Earth axis. It is why the magnetic pole is moving toward Siberia. It is following the axis line. If this tilt continues on it's path then theory would have the Mid Atlantic Ridge pulling apart at some point and the Pacific Plate forcing under Asia even further. Keep alert on the magnetic pole as it keeps aligning with the axis. All theory by the way. I suspect a huge Quake on the East Coast of the United States soon as well as the North African Plate. The Caribbean Plate could snap from the gravity of this tilt.
Imagine another Megathrust like the March 11, 2011 earthquake off the Pacific coast of Tōhoku in the same spot that generates another Tsunami. Keep Reactor 4 in mind.
I keep suspecting a rumbling all over the entire globe. In a way, there has been with all these News reports of odd sounds and rumblings in obscure areas. They blame it on fracking when in fact something is happening to our planet. But we must go on with the show or utter chaos would ensue. Tick Tock. You better get out there and live as if it were your last day. The Earth is an awesome paradise.