I-MAG STS Corporation
O it's "Thin red line of 'eroes" when the drums begin to roll.
from Rudyard Kipling's poem Tommy
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The classical explanation of seismic aftershocks has been the primary
aftershock is about 75 to 80% of the Richter strength of the primary event,
so a primary of 8.0 should have its most powerful aftershock between 6.0 and
6.4. Then later aftershocks decrease in strength and occur farther apart in
time. It is useful then to analyze the aftershocks to see if there are clusters by
strength and location. One can build up what looks like a wide but shallow tree
of groups of ostensibly related aftershocks. Then one may wish to determine if
the various groups are actually aftershocks or separate clumps of earthquakes.
A reasonable example of this is Chile where the struggle is to determine what
the actual ongoing impact of the recent large event (8.8 February 27, 2010). In
Japan there was an anomalous cluster of 10 Richter events very close in space
and time. Then a 7.3 on 3/9. This was followed by 13 more events including an
out of pattern 5.9 and a 6.0. Then a day with no activity. The non-infamous 9.0
struck on 3/11 followed by 6.4, 6.4, 6.8 and 7.1 (!) events and 360 more
including 2 6.6s and a 6.4 starting at 2011/03/22 07:18 UTC. Clearly,
something far removed from theory is going on here. To account for the
staggering number of events and their location west of the Pacific Plate's edge,
we hypothesize a mantle plume.