Earthquake (6)

Living in eastern Japan is almost like living on shipboard, the way the ground beneath us seems to roll without rest. On some days, the after-shocks from the March 11 quake seem bigger than brand-new earthquakes. Experts say that is only to be expected. After-shocks are, by definition, a degree or so smaller than the original quake, and when the original one is huge, the after-shocks are also huge.

Here is a part of a Q/A from the Japan Times, with Yoshiro Ota of the Japan Meteorological Agency, written by Minoru Matsutani:

(1) Why do aftershocks occur?

Because tectonic plates and faults try to stabilize ground conditions that have been greatly altered by a huge earthquake.


(2)Why do we have so many big aftershocks?

The magnitude of the largest aftershocks tend to be about 1.0 magnitude lower than the main quake, which was 9.0, said Yoshiro Ota of the Meteorological Agency.

"People tend to think aftershocks are small. But a magnitude 8 is huge. Magnitude 7 is also huge, so we should be very careful," Ota said.


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http://search.japantimes.co.jp/mail/nn20110414a5.html