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Author Topic: Time difference between and Earthquake and an Aftershock.  (Read 7106 times)

paul.fr

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Monday Night (UK time) there were two earthquake of note. The first was A magnitude of 7.6 and struck off India’s Andaman Islands.




The second earthquake , a 6.4 magnitude, struck Japan only minutes later.




According to This news item:


Quote
A seismologist at the United States Geological Survey told BNO News that the earthquake appears to be an aftershock to the major earthquake in December 2004, which sparked a deadly tsunami that killed hundreds of thousands of people. He said aftershocks can continue for years.

Can you really have an aftershock 4 and a half years later? Could the first quake have triggered the second?


 

Offline JimBob

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Time difference between and Earthquake and an Aftershock.
« Reply #1 on: 12/08/2009 16:55:01 »
If the USGS says it, it MUST be right!

It is a matter of scale. If you try to move a piano it takes a little force to shove it a few feet. To move a piece of material the size of a football stadium, it make take a few people and a machine or two - and a little more time. For a piece of the earth's crust it takes a lot longer to get it moving and then to stop it. In fact it normally does not stop. And the time period it takes to move it also increases with the size.

So YES - you can have an aftershock 4.5 years after a major earthquake. 

 

Offline LeeE

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Time difference between and Earthquake and an Aftershock.
« Reply #2 on: 12/08/2009 17:29:07 »
The 2004 Boxing day quake and the recent 7.6 quake seem to be at opposite ends of the same fault.  I don't know if it's appropriate to describe the second quake as an aftershock to the first though.  I think it may come down to whether the stress that was relieved by the recent quake at the northern end was present when the 2004 boxing day quake occurred, or whether that stress had built up since then.  If the stress was already present in 2004 then it might be fair to say that the recent quake was just the completion of the earlier quake.

If this is so though, and it was known that the stresses were already high in this region, then I would imagine that many people were expecting this quake.  The USGS seismologist probably does know what (s)he's talking about.

The recent quake near Japan is several plates away, so is probably not connected to the recent quake off the Andaman Isles.
 

Offline JimBob

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Time difference between and Earthquake and an Aftershock.
« Reply #3 on: 14/08/2009 17:41:17 »
The process is called "unzipping."  As stress is relieved in one area, it is concentrated in the the next area up the line. The most famous and well documented is the North Anatolian Fault. There have been a series of earthquakes moving from east to west across the top of Turkey, separated by about a 20 year period.

When the Boxing Day earthquake happened I distinctly remember this process being discussed on a Public Broadcasting Television show - Smithsonian World I believe. The prediction was that in a short period of time the quakes would move progressively north.

 

Offline LeeE

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Time difference between and Earthquake and an Aftershock.
« Reply #4 on: 14/08/2009 18:13:28 »
Ah - now that you mention it, the phase 'unzipping' in this context does ring a bell.  I remember reading about the progressive series of quakes through Turkey as well now.

Thanks for the reminder.
 

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Time difference between and Earthquake and an Aftershock.
« Reply #4 on: 14/08/2009 18:13:28 »

 

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