The scene of destruction in Japan due to the large magnitude 9 earthquake and resulting tsunami has shocked and saddened us all - especially since I spent some time in Sendai and the surrounding area in 1999. And the photographs of the aftermath are heart breaking.
What has also astonished me are the huge numbers of aftershocks in the area.
Using data from the US Geological Survey, I have plotted a graph of the seismic activity around Japan over the past week (see below). The strength and number of aftershock is astounding.
Remember, a magnitude 4-4.9 earthquake causes noticeable rattling, and for every unit you go up the scale, an earthquake is 10 times stronger. A magnitude 5 quake, being ten times more powerful than a magnitude 4, can already do damage. The magnitude 9 quake that Japan experienced last week is 10,000 times stronger than a magnitude 5 quake - almost incomprehensible.
The graph shows...
- 1 Mag 9 Earthquake
- 1 at Mag. 7.1
- 37 between Mag. 6.0-6.8
- 258 between Mag. 5.0-5.9
That's 300 earth-quakes, all of which could cause structural damage, in just one week. Terrifying.
One wonders when will these earth-quakes end?
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