As earthquakes go, tsunami earthquakes are rather weak. They occur in shallow depths in the ocean and are generally small in magnitude. However, these small earthquakes often produce powerful and surprisingly large tsunamis. Even earthquakes measuring as small as 5.6 on the Richter scale generates tsunami waves up to ten meters high when they reach land. With a global network of seismometers, researchers have been able to detect small earthquake virtually anywhere. However, the challenge lies in discerning why some small magnitude quakes cause tsunamis while others do not.
A new study that was published in the journal Earth and Planetary Science Letters has revealed that tsunami earthquakes may not be completely random, but rather may be caused by extinct undersea volcanoes causing a "sticking point" between two sections of tectonic plates. Researchers from the Imperial College of London and GNS Science in New Zealand used geophysical data that was collected originally for gas and oil exploration. They also used some historical accounts and eyewitness statements of previous tsunami earthquakes dating back as far as 1947. As tsunami earthquakes were only identified by scientists 35 years ago, research on these events is a bit of a rarity. Upon further inspection, the team located two extinct volcanoes off the coast of Poverty Bay and Tolaga Bay that have sunk beneath the crust off the coast of New Zealand in a process called subduction.
Their research of these areas found that the volcanoes prove as a sort of sticking point between the Pacific tectonic plate and the New Zealand tectonic plate. When these two points become unstuck, as they did in 1947, it releases a lot of energy and causes massive movement on the ocean floor. This, in turn, causes the formation of large tsunamis. This research provides valuable insight into the event and now the scientists watching those seismometers around the world will be able to better pinpoint when an underwater earthquake is likely to produce a large tsunami.