Japan Aftershocks: More Than One-Thousand Aftershocks So Far

The aftershock map to the right is impressive: every dot is an aftershock of the 9.0 mega-quake that rocked Japan and created a tsunami on March 11, 2011.

But guess what? This image was created just 24 hours after that quake. By that point there had ‘only’ been about 100 aftershocks.

Now that number is over 1,000.

I can only imagine how fried your nerves would be if you live in certain parts of Japan. The ground refuses to stop shaking. At least that’s how it must seem.

Japan Quake Aftershock Numbers: Aftershocks Of Magnitude 4.0 Or Greater

The numbers below do not include all aftershocks. Instead, just those of magnitude 4.0 and greater.

 I searched high and low for these numbers on my favorite quake sites, on Google, everywhere. And when I came up empty handed, I emailed my contacts at the U.S. Geological Survey (the USGS).

Paul Laustsen, at the USGS, was kind enough to reply: “To answer your question directly, it appears there have been 1,066 magnitude 4.0 or greater aftershocks since the m9 mainshock on March 11.”

And guess what? That number is climbing every single day. I’ve been tracking the aftershocks by hand since Paul’s email of April 6, 2011. The very next day (April 7) Japan had a magnitude 7.1 aftershock  that did more damage and triggered another tsunami warning. You probably heard about it. But it was just one of eight aftershocks that day–the others didn’t make the news.

So by doing the math thru April 10, 2011 the total number of aftershocks greater than magnitude 4.0 stands at 1,096. It’s hard to believe so many could happen by the one month anniversary of  the Japan earthquake and tsunami.

 Wow. Someday, Oregon, Washington and Northern California will experience the same kind of nerve frying situation after the subduction zone ruptures off our coast line.  Here’s more about the risk of a northwest mega-quake that will impact cities like Seattle, Washington and Portland, Oregon and coastlines around the world because of the resulting tsunami. 

If there is a silver lining to this story, it’s this: overall, the number of aftershocks is decreasing and will continue to do so. That’s the way these things work. Also, the average  magnitude of these quakes will continue to decrease. So fewer people will feel them. Still, there’s likely to be at least a few more large quakes that add to the damage. And these can happen years after the initial Japan quake.

Here’s why the aftershocks keep on happening, in human and (watered down) scientific terms.