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Earthquakes and Tree Rings
Name: Lew
Status: Other
Grade: Other
Location: FL
Country: United States
Date: Spring 2010
Question:
I understand that the occurrence of past earthquakes can
be detected in tree rings and in coral growth rings. I assume that
there is an interruption in the ring structure, but how can a
researcher be confident that it is caused by an earthquake. In other
words, does the earthquake leave a unique signature?
Replies:
Hi there,
In the vast majority of cases tree rings or coral growth rings will
show earthquakes and other natural events because the event in some
way interrupts the growth (of the tree or the coral)
An earthquake on land may well dislodge branches and cause damage to
trees, which can be seen in the growth rings, or the tree may be
killed outright, in which case fossil stump will all show a ring set
which finishes at the time of the earthquake. In the oceans, as well
as damage, there may be increased turbidity caused by stirring
sediment up from the sea bed. This can show in the coral as dirty
layers in the growth rings.
Similarly, fire and volcanoes can cover the tree or the coral in ash
which becomes incorporated in the growth rings to be seen later. If
there is sufficient ash fall the growth of the tree may be hindered or
even stopped for a season or two - and this too will be reflected in
the rings. In some cases rings may be missing altogether! See
http://vulcan.wr.usgs.gov/Projects/TreeRings/tree_ring_dating.html
Anything which can affect the growth of the tree - be it sunlight,
temperature, nutrient levels, grazing, fire, smog, smoke, water or
even just dust in the air, can all leave traces in the tree rings
which are produced.
Nigel S
Tennant Creek High School
AUSTRALIA
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