Rain, the means of life on earth, can also fuel chaos – this is an undeniable fact humans have come to accept. A new study shows that the bitter aspect of rain is even more threatening than we would allow ourselves to think: water sent down from above can also promote intense earthquakes. The paper is published in Earth and Planetary Science Letters.
Rainwater and snowmelt have the ability to trigger earthquakes on a tectonic fault in New Zealand, the Alpine Fault, observe a team of scientists. The latter wanted to find the origin of the water flowing through Alpine Fault, and when they attempted to reach to the source, they discovered that over 99% of that water was the result of precipitation. Water triggering tremors in the Earth is not something new; rather, researchers have suggested in the past that underground fluids can play a role in causing earthquakes. However, what remained unknown until now was the origin of these liquids.
They were able to trace the origin-water by analysing the minerals deposited in the rocks, said to be brought by water. The relative abundance of helium (found in hot springs located nearby), and oxygen and hydrogen isotopes constituting the water molecules were also measured. These figures led the scientists to their conclusion that this water comes from rainfall and meltwater concentrated by the Southern Alps which are found in the vicinity of the Alpine Fault.
The researchers also found out that the fault becomes an impermeable dam for the water that ends up getting trapped there. As a consequence, “large fluid pressures” are set up by the fault itself, thereby leading to earthquakes, explains geologist Catriona Menzies from the University of Southampton, one of the study authors.
How do these trapped fluids trigger earthquakes? According to Menzies, this happens because the fluids modify the strength of the rock, and generate opposing forces to those keeping the two sides of the fault together.