Extinct Undersea Volcanoes May Cause Rare Tsunami Earthquakes

Rare tsunami earthquakes can create massive tsunamis, impacting coastlines and causing devastating losses. Now, scientists may have found out the causes for and warning signs of these earthquakes, which could lead to better detection measures in the future.

Tsunami earthquakes occur at relatively shallow depths in the ocean. In fact, they're somewhat small in terms of their magnitude, but they can create very large tsunamis; earthquakes that only measure 5.6 on the Richter scale can generate waves of up to 10 meters when they reach the shore. For example, in 1992, a magnitude 7.2 tsunami earthquake off of the coast of Nicaragua in Central America caused the deaths of 170 people. Another earthquake off of the coast of Java, Indonesia in 2006 that also measured 7.2 caused the deaths of 637 people. Needless to say, it's important to develop better prediction methods in order to prevent these sorts of tragedies.

In this case, the scientists used geophysical data collected for oil and gas exploration in addition to historical accounts from eye witnesses relating to two tsunami earthquakes, which happened off of the coast of New Zealand's north island in 1947.

The researchers located two extinct volcanoes off of the coast of Poverty Bay and Tolaga Bay that have been squashed and sunk beneath the crust off the coast of New Zealand in a process called subduction. These volcanoes likely provided a "sticking point" between a part of the Earth's crust called the Pacific plate, which was trying to slide underneath the New Zealand plate. This, in turn, caused energy to build which was then released and resulted in tsunami earthquakes.

"Tsunami earthquakes don't create massive tremors like more conventional earthquakes such as the one that hit Japan in 2011, so residents and authorities in the past haven't had the same warning signals to evacuate," said Rebecca Bell, one of the researchers, in a news release. "These types of earthquakes were only identified a few decades ago, so little information has been collected on them. Thanks to oil exploration data and eyewitness accounts from two tsunami earthquakes that happened in New Zealand more than 70 years ago, we are beginning to understand for the first time the factors that cause these events. This could ultimately save lives."

Currently, scientists are working to develop a better warning system for residents in New Zealand. In addition, they plant to conduct new geophysical surveys over the sites of other sinking volcanoes in order to better understand their characteristics.

The findings are published in the journal Earth and Planetary Science Letters.