The most obvious evidence of an earthquake occurs when you see the changes it has left behind. However, there are other indicators of seismic shifts that are not as obvious and they are not found in the geoological record.
Scientists discovered an unexpected consequence of earthquakes. This is one that lasts well beyond the time after the aftershocks have subsided: A detectable increase in tree height due to earthquake-triggered changes in groundwater availability.
Although it is well-known that earthquakes can alter the fortunes of trees, there are still many things we don't know. For example, how earthquakes affect tree growth and how much information is stored in their living, biological archives.
The thinking is simple.
A team of researchers, led by Christian Mohr, a German hydrologist, explained that large earthquakes can increase water flow, elevate groundwater levels and give plant roots more water access in water-limited environments.
"If tree growth is restricted primarily by water, trees should theoretically record hydrological responses for earthquakes by changing growth rates."
These ideas were explored and tested by the researchers. They hypothesized that groundwater supply changes from earthquakes would encourage tree growth near valley streams, but inhibit it if the trees are higher up on hillsides. The researchers then studied Pinus radiata pines in Chile to determine the effects of the 8.8-magnitude earthquake in 2010.
Analysing tree cores from both the valley floor and hillslope ridges revealed that some trees experienced temporary increased growth following the earthquake. This was based on both tree ring evidence (increased area of trees) and the ratio of carbon isotopes within the trees' cells. This gives a cellular perspective on aspects such as tree growth and health.
However, trees on the slopes did not fare as well over the same time period. This supports the hypothesis of the researchers. The team also acknowledges that the overall earthquake effect was minimal and only lasted for a few weeks.
The researchers still believe that these techniques can be applied in the field. Their findings indicate that post-seismic changes to the area of the lumen and the carbon isotope ratios can help to study tree growth as well as photosynthetic responses in earthquakes.
This could give us a new tool for studying earthquakes from the past.
Researchers write that details in wood anatomy and isotopes could offer a tree-based approach to paleoseismology, beyond just considering width.
These findings were published in JGR Biogeosciences.