Local tsunamis and subduction zones
A lot of people have asked us why we are always mentioning the (important)Â relation in between the epicenter and an eventual subduction zone (one tectonic plate subducting another one).
The fear of Sea-slide Tsunamis or Mega-tsunamis are the answer.
Very strong earthquakes can devastate large portions of the submarine slopes and accordingly generate a local tsunami. Almost every NOAA report of a powerful seaquake is mentioning that even when NO widespread tsunami is likely, the chance on a local tsunami is always present.
A submarine landslide, rock fall, or ice fall can trigger a tsunami by displacing large amounts of water.
As a result, the water level rises generating a massive wave, or tsunami.
Underwater landslide tsunamis - Courtesy http://geol105naturalhazards.voices.wooster.edu
Megatsunami
The technical term for a tsunami caused by landslides, is megatsunami.
Megatsunamis have considerably higher amplitude than typical tsunamis because the amount of water displacement increases the wave size more than a submarine earthquake.
The USGS and UK Institute of Oceanographic Studies completed a study on the submarine landslides present in Hawaii. By using GLORIA, a type of long range sonar, they were able to determine that there were considerable amounts of sedimentary build up as a result of landslides. These findings supported the hypothesis that submarine landslides could result in massive tsunamis.
There have been several tsunamis believed to be a direct result of a submarine landslide. One of the most destructive of these, was the 1998 tsunami in Papua-New Guinea.
An underwater earthquake with a magnitude of 7.1 was believed to have displaced submarine sediments, resulting in a landslide and, ultimately, a tsunami.
October 25, 2010 Mentawai Tsunami
The powerful M 7.7 earthquake, which killed several hundred of people, was merely a local phenomena affecting only the Mentawai islands. The power of the tsunami was not predicted in most theoretical models.
The specialized institutes like GDACS and NOAA, who are doing incredible great work in predicting potential risks, had calculated only limited wave heights towards the Pagai islands.
Eyewitness reports did mention massive waves of several meters high.
It will be a job for scientists to find out why the theoretical models did fail.
Earthquake Report emphasizes the coincidence of the subduction zone epicenter and the bigger than calculated tsunami waves.
Google map cutout of the Pagai tsunami earthquake and epicenter
Text source for certain content :
http://geol105naturalhazards.voices.wooster.edu/
http://landslides.usgs.gov
QuakeSOS is a FREE iPhone application developed by Armand Vervaeck (SOS Earthquakes), the creator and main contributor to Earthquake Report. The Application simplifies immediate group communication to friends and family members (with your exact GPS location) and is constantly feeding the users with “Earthquake Report” news. Together with your own family and friends, QuakeSOS will be your closest earthquake friend.
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Quake-Maps.com was also created by SOS Earthquakes. Quake-Maps.com makes it easy to let the world know which shaking people have experienced during the earthquake. Quake-Maps.com gives also the opportunity to write some additional text. Filling up the form takes only 1 minute. Quake-Maps.com gives an overview of all the resent earthquakes and let you even go back in time and retrieve earthquakes of a certain date in the past.
