2011 Off the Pacific Coast of Tohoku earthquake, Strong Ground Motion

[ssobhan]

Hi all

Preliminary information on the recorded strong ground motions during the 2011 Off the Pacific Coast of Tohoku earthquake available in the following link:

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Regards

[iceman84]

I find those values of the PGA (between 1 and 3g) truly astonishing.

[iceman84]

A link for downloading some strong ground motion records of Tohoku earthquake:

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[LiviuM]

Hello can somebody please explain me why earthquakes in japan don't stop after so many days? Starting from 9.0 mag they have earthquakes at 10-30 minutes time interval.

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[onest30]

Hello Livium,
You see, major earthquakes are not most of
the time alone. This means that, whenever a great earthquake
occurs this will be come accompanied by other earthquakes, before or
after the "big one".
The ones occurring before are technically speaking so called "foreshocks"
and the ones occurring after the big one are so called "aftershocks".

In the case of the recent, unfortunate Japanese earthquake there seems to have
occurred two foreshocks before the big one (M=9.0).
Then a lot of aftershocks have occurred.

The reason of such aftershocks is somehow simple to explain, imagine something
that is at rest (in this case the plates). What the earthquake does is to generate a sudden slip over a place of
the plates that was "locked" during many years. In other words, it generates a sudden movement of one plate with respect the other. So after the earthquake occurs, the fault plane/plates contact is unstable which causes aftershocks until the plates get at rest once again.
And then the cicle begins again. loading("at rest")+energy release(earthquake/unloading)+rest(loading process begins again)

I hope this helps

Regards

[LiviuM]

Thank you very much onest30 I totally agree.
I know the basics about earthquakes, tectonic plates and even if I design earthquake resistant buildings I have never imagined that the aftershocks could last for so long.
I was thinking of a few hours or maybe even a day but one week and so frequent, too much for my imagination, and a so simple explanation. If I think about those people that are still being shacked, it's sad and frightening.