Some trees 'record' earthquakes by growing faster
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A recent study in the Journal of Geophysical Research: Biogeosciences provides new evidence that earthquakes can alter tree growth patterns by changing groundwater flow and soil permeability.
The research greatly improves the precision of efforts to date past seismic activity.
"They refine the chronology, the time of the earthquake, on a very fine scale, within weeks. It's very hard to catch this kind of signal with a tree," said Irina Panyushkina of the University of Arizona's Laboratory of Tree-Ring Research, who was was not involved in the study.
By studying cell sizes and carbon isotope ratios in trees affected by the 2010 Maule 8.8 magnitude earthquake in Chile, the authors found tree growth in dry regions increases downslope and decreases upslope following seismic events.
Normally, Chilean pines have little water to pump during the dry season, so they conserve energy by growing thinner versions of their water-transporting vessels, called tracheids. Thus, a sudden change in dry-season tracheid diameters likely means the trees need to pump a lot of water. Lacking any precipitation change, that moisture must come from changes in the water table and soil permeability.
Similarly, the ratios of carbon isotopes in wood cellulose rebalances based on growth spurts because trees take up more carbon-12 than larger, heavier carbon-13 during photosynthesis.
"They right away attributed this very unusual behavior in those two parameters, or signature, to the earthquake, and basically described the mechanism of how the earthquake changed the hydrology of the region, and how the tree responded to that," said Panyushkina.
Panyushkina praised the research for its precision and methodology, and said its combination of techniques exemplifies where the field is headed.
"We could just say it happened, for example, in the year 2014. In this case, the guys can say that it happened in the first and second week of June 2014."
