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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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