Heavy Rain Can Help Trigger Earthquakes

Earthquakes are an unpleasant fact of life, they occur worldwide and there are several quakes, some serious each year. Most quakes occur with an ocean floor epicenter, some will occur across land in proximity to population centers and with differing levels of severity. Where it rains, it apparently rumbles underground. New research in New Zealand suggests that intense rainwater and melting snow actually encourage earthquakes along a New Zealand tectonic fault known as the Alpine Fault.

If this is proven to be true then it establishes a link between heavy rainfall and the likelihood of earthquake or tremor as the ground moves.

Heavy Rain Can Help Trigger Earthquakes

New Zealand’s Alpine Fault water flow shows that more than 99 percent of the water flowing through the New Zealand Alpine Fault fault came from direct rainfall, as reported by researchers in the April 19 edition of  Earth and Planetary Science Letters. Previously scientists were always aware that that underground fluids help trigger quakes. Yet in many cases it was never clear where these underground waters actually came from. For example these fluids could originate from lakes, rivers, underground caves or rainwater. The possibilities as to the origin of these waters were always varied.

In this case in New Zealand, the nearby Southern Alps direct heavy rainfall and melting snow on top of the Alpine Fault. Within the fault the water is trapped and it permeates into the ground. The fault “essentially [is] promoting its own large fluid pressures that can lead to earthquakes,” says study coauthor and academic Catriona Menzies, a researcher and geologist at the University of Southampton in England.

Identifying source of all this flowing water into the fault will help scientists better predict the fault’s seismic cycle, she says. This could be a powerful tool in predicting earthquakes in other areas of the world and in protecting valuable cities and their population; cities such as San Francisco which lives under the constant threat of serious earthquake.

New Zealand of course is a country that sits on the boundary where the Australian and Pacific tectonic plates collide. As the plates move against each other the collision of energy and friction generates a powerful earthquake along the Alpine Fault. The quake hits here around once every 330 years. The most recent serious quake caused by the Alpine Fault in New Zealand was in 1717. This plate movement also gradually formed the Southern Alps as the two tectonic plates forced the landmass upward.

It is here that moist air condenses when rising over the mountains, which causes heavy rainfall that typically exceeds 10 meters each year. The researchers Menzies and colleagues naturally pondered on just how much rainwater enters the Alpine Fault zone. Fluids within a fault help encourage quakes by altering the composition of rock and soil and by interfering with the natural forces that hold two sides of a fault together. In essence the rainwater destabilizes the rock within the fault lines making it more prone to movement and therefore generate a resulting earthquake or tremor.