June 28, 2014
Impact Of Undersea Volcanoes On Tectonic Plates Possibly Responsible For Tsunami Quakes
redOrbit Staff & Wire Reports - Your Universe Online
“Sticking points” in the Earth’s tectonic plates caused by extinct undersea volcanoes could be responsible for producing tsunami earthquakes, a discovery which could lead to improved detection of these rare seismic events.
Tsunami earthquakes typically occur at relatively shallow ocean depths and are typically of lower magnitude. However, they can create extremely large tsunamis, with earthquakes measuring as little as 5.6 on the Richter scale generating waves that can be up to 10 meters in size by the time they reach the shore, the authors said.
While a global network of seismometers allows even the smallest earthquakes to be detected, it has been difficult to determine which low-magnitude events are likely to spawn large tsunamis. Now, in research appearing in the journal Earth and Planetary Science Letters, researchers from Imperial College London and GNS Science report they may have found a solution.
In their paper, the study authors analyzed geophysical data originally collected for oil and gas exploration purposes, as well as historical accounts from eye-witnesses to a pair of tsunami earthquakes that took place off the coast of the north island of New Zealand in 1947. Since tsunami earthquakes were only first identified less than four decades ago, little detailed information about these incidents is available.
[ Watch the Video: What is a Tsunami? ]
The investigative team located two extinct volcanoes off of the coast of Poverty Bay and Tolaga Bay, each of which has been squashed and sunk beneath the crust of the New Zealand coast through the process of subduction. They believe that the volcanoes prevented the Pacific tectonic plate from sliding beneath the New Zealand plate.
As a result, energy began to build up until it was released in 1947, which caused the plates to separate, the Pacific plate to move, and the volcanoes to become buried beneath New Zealand. The energy release from the two plates was unusually slow and took place close to the seabed, causing large movements on the sea floor and ultimately generating very large tsunami waves, the researchers explained.
“All these factors combined, say the researchers, are factors that contribute to tsunami earthquakes,” the university explained in a statement. “The researchers say that the 1947 New Zealand tsunami earthquakes provide valuable insights into what geological factors cause these events. They believe the information they’ve gathered on these events could be used to locate similar zones around the world that could be at risk from 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,” noted Dr. Rebecca Bell of the Imperial College London Department of Earth Science and Engineering. “These types of earthquakes were only identified a few decades ago, so little information has been collected on them.”
Eyewitnesses to these tsunami earthquakes also described the type of ground movement that took place, which could be used by seismologists to help develop early warning systems for communities that could be affected by these events. That information, combined with the oil exploration data, is making it possible for them to better understand the factors that cause tsunami quakes, potentially saving lives in the process, Dr. Bell added.
“The researchers are already working with colleagues in New Zealand to develop a better warning system for residents,” the university concluded. “In particular, new signage is being installed along coastal regions to alert people to the early warning signs that indicate a possible tsunami earthquake. In the future, the team hopes to conduct new cutting-edge geophysical surveys over the sites of other sinking volcanoes to better understand their characteristics and the role they play in generating this unusual type of earthquake.”