Tuesday, July 1, 2014

Extinct undersea volcanoes squashed under Earth's crust cause tsunami earthquakes

Via The Watchers, 28 June 2014


New research has revealed the causes and warning signs of rare tsunami earthquakes, which may lead to improved detection measures.

Tsunami earthquakes happen at relatively shallow depths in the ocean and are small in terms of their magnitude. However, they create very large tsunamis, with some earthquakes that only measure 5.6 on the Richter scale generating waves that reach up to ten metres when they hit the shore.

A global network of seismometers enables researchers to detect even the smallest earthquakes. However, the challenge has been to determine which small magnitude events are likely to cause large tsunamis.
In 1992, a magnitude 7.2 tsunami earthquake occurred off the coast of Nicaragua in Central America causing the deaths of 170 people. Six hundred and thirty seven people died and 164 people were reported missing following a tsunami earthquake off the coast of Java, Indonesia, in 2006, which measured 7.2 on the Richter scale.

The new study, published in the journal Earth and Planetary Science Letters, reveals that tsunami earthquakes may be caused by extinct undersea volcanoes causing a "sticking point" between two sections of the Earth's crust called tectonic plates, where one plate slides under another.

The researchers from Imperial College London and GNS Science in New Zealand used geophysical data collected for oil and gas exploration and historical accounts from eye witnesses relating to two tsunami earthquakes, which happened off the coast of New Zealand's north island in 1947. Tsunami earthquakes were only identified by geologists around 35 years ago, so detailed studies of these events are rare.
The team located two extinct volcanoes off 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.

The researchers suggest that the volcanoes 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 caused a build-up of energy, which was released in 1947, causing the plates to "unstick" and the Pacific plate to move and the volcanoes to become subsumed under New Zealand. This release of the energy from both plates was unusually slow and close to the seabed, causing large movements of the sea floor, which led to the formation of very large tsunami waves.

All these factors combined, say the researchers, are factors that contribute to tsunami earthquakes. 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. Eyewitnesses from these tsunami earthquakes also describe the type of ground movement that occurred and this provides valuable clues about possible early warning signals for communities.

Continue to the full article here,
http://thewatchers.adorraeli.com/2014/06/28/extinct-undersea-volcanoes-squashed-under-earth-s-crust-cause-tsunami-earthquakes-according-to-new-research/


2 comments:

Kiwi25 said...

Interesting...I live along that coast tho well inland (BOP, NZ) and have been to a place where that wave came in and there are pictures of people with fish that were washed up. As they say there has been huge coastal development since 1947 and such waves today would cause huge loss of life and damage. There would be little time to react as the subduction zone is quite close to the coast.
Right now you still pay a big price premium for a house right on the beach.

Kiwi25 said...

Here is a link to a local report http://www.stuff.co.nz/dominion-post/news/10225747/Scientists-solve-riddle-of-Gisborne-tsunami