A new way to predict earthquakes in Iceland has been found, as chemical changes in groundwater leads to major tremors. Researchers found that before major earthquakes, the amount of sodium and silicon in the island's groundwater drastically increased.

The study suggests that the ground changes shape before an earthquake, allowing deeper, sodium and silicon-rich groundwater to merge with the existing water table. This is the first time the connection has been officially made, and researchers believe this could be the key to unlocking the mystery of predicting Icelandic seismic activity.

"Before an earthquake, the ground warps and bends," said Margareta Andrén, lead author of the study. "The shifting ground could open up new surfaces to groundwater. This influx of new water could explain the chemical changes before the quake."

The research, presented at the 2015 American Geophysical Union Fall Meeting, used groundwater samples from northern Iceland, stretching back to 2008. Weekly samples were taken from the Tjörnes Fracture Zone by the researchers, to analyse the amount of dissolved sodium and silicon in the water. They then compared these results to the timings of earthquakes.

They found that the amount of the chemicals in the water samples has been steadily decreasing over the past seven years. However, there were two occasions when the chemicals spiked, increasing rapidly. On both occasions, they were followed by magnitude five or higher earthquakes within six months.

Previous investigations have suggested the link between groundwater chemicals and seismic activity, but over the course of the studies, no more than one earthquake was analysed. That means this new study is more reliable, and can lead scientists to begin thinking about predicting future earthquakes.

"Having two earthquakes makes us very confident in our data," said Andrén. She did, however, stress that this does not mean earthquakes can be predicted indefinitely now: "We need more samples to do that."

Evidence suggests that groundwater chemicals drastically increased in other parts of the world, too. Investigations showed this was the case for the 1995 Kobe earthquake – which killed 6,400 people – but the study showed just one isolated incident, reducing its reliability.