NASA Study Challenges Long-held Tsunami Formation Theory May 18, 2017

[Tsunami waves hitting the coast of Minamisoma in Fukushima prefecture, Japan. Credit: Sadatsugu Tomizawa CC BY-NC-ND 2.0]

A new NASA study is challenging a long-held theory that tsunamis form and acquire their energy mostly from vertical movement of the seafloor. An undisputed fact was that most tsunamis result from a massive shifting of the seafloor — usually from the subduction, or sliding, of one tectonic plate under another during an earthquake. Experiments conducted in wave tanks in the 1970s demonstrated that vertical uplift of the tank bottom could generate tsunami-like waves. In the following decade, Japanese scientists simulated horizontal seafloor displacements in a wave tank and observed that the resulting energy was negligible. This led to the current widely held view that vertical movement of the seafloor is the primary factor in tsunami generation.

In 2007, Tony Song, an oceanographer at NASA’s Jet Propulsion Laboratory in Pasadena, California, cast doubt on that theory after analyzing the powerful 2004 Sumatra earthquake in the Indian Ocean. Seismograph and GPS data showed that the vertical uplift of the seafloor did not produce enough energy to create a tsunami that powerful. But formulations by Song and his colleagues showed that once energy from the horizontal movement of the seafloor was factored in, all of the tsunami’s energy was accounted for. Those results matched tsunami data collected from a trio of satellites -the NASA/Centre National d’Etudes Spatiales (CNES) Jason, the U.S. Navy’s Geosat Follow-on and the European Space Agency’s Environmental Satellite.

Further research by Song on the 2004 Sumatra earthquake, using satellite data from the NASA/German Aerospace Center Gravity Recovery and Climate Experiment (GRACE) mission, also backed up his claim that the amount of energy created by the vertical uplift of the seafloor alone was insufficient for a tsunami of that size.

“I had all this evidence that contradicted the conventional theory, but I needed more proof,” Song said.

His search for more proof rested on physics — namely, the fact that horizontal seafloor movement creates kinetic energy, which is proportional to the depth of the ocean and the speed of the seafloor’s movement. After critically evaluating the wave tank experiments of the 1980s, Song found that the tanks used did not accurately represent either of these two variables. They were too shallow to reproduce the actual ratio between ocean depth and seafloor movement that exists in a tsunami, and the wall in the tank that simulated the horizontal seafloor movement moved too slowly to replicate the actual speed at which a tectonic plate moves during an earthquake.

“I began to consider that those two misrepresentations were responsible for the long-accepted but misleading conclusion that horizontal movement produces only a small amount of kinetic energy,” Song said.

Building a Better Wave Tank

To put his theory to the test, Song and researchers from Oregon State University in Corvallis simulated the 2004 Sumatra and 2011 Tohoku earthquakes at the university’s Wave Research Laboratory by using both directly measured and satellite observations as reference. Like the experiments of the 1980s, they mimicked horizontal land displacement in two different tanks by moving a vertical wall in the tank against water, but they used a piston-powered wave maker capable of generating faster speeds. They also better accounted for the ratio of how deep the water is to the amount of horizontal displacement in actual tsunamis.

The new experiments illustrated that horizontal seafloor displacement contributed more than half the energy that generated the 2004 and 2011 tsunamis.

[Credit: Gabriel Andrés Trujillo Escobedo, CC BY 2.0]

“From this study, we’ve demonstrated that we need to look at not only the vertical but also the horizontal movement of the seafloor to derive the total energy transferred to the ocean and predict a tsunami,” said Solomon Yim, a professor of civil and construction engineering at Oregon State University and a co-author on the study.

The finding further validates an approach developed by Song and his colleagues that uses GPS technology to detect a tsunami’s size and strength for early warnings.

[Credit: Petr Malyshev / Fotolia]

The JPL-managed Global Differential Global Positioning System (GDGPS) is a very accurate real-time GPS processing system that can measure seafloor movement during an earthquake. As the land shifts, ground receiver stations nearer to the epicenter also shift. The stations can detect their movement every second through real-time communication with a constellation of satellites to estimate the amount and direction of horizontal and vertical land displacement that took place in the ocean. They developed computer models to incorporate that data with ocean floor topography and other information to calculate the size and direction of a tsunami.

“By identifying the important role of the horizontal motion of the seafloor, our GPS approach directly estimates the energy transferred by an earthquake to the ocean,” Song said. “Our goal is to detect a tsunami’s size before it even forms, for early warnings.” The study is published in Journal of Geophysical Research — Oceans.

From Samson Reiny, NASA Earth Science News Team

For WeatherNation: Meteorologist Mace Michaels

Leave a comment

Your email address will not be published. Required fields are marked *

Tweets

Looking busy in St. Joe, Missouri as many get ready for the #SolarEclipse. We are talking about the forecast on Wea… https://t.co/o61KhXLTO9

6 hours ago by WeatherNation

UPDATED: Storm system brings risk of #severe weather across the upper midwest today & Monday, systems pushes east o… https://t.co/f7UCaj02qK

10 hours ago by WeatherNation

Storm system will bring elevated risk of #severe weather across the upper midwest Monday, systems pushes into much… https://t.co/e6fVrDWN4G

12 hours ago by WeatherNation

People are flocking to #Casper, WY to see #SolarEclipse2017 Heavy traffic is expected near the path of totality so… https://t.co/dmg5JNud1u

14 hours ago by WeatherNation

The storm threat continues for some spots on Sunday. Get your AM edition of WeatherNation with all the details!… https://t.co/G8VzJOgTtG

23 hours ago by WeatherNation

What's the forecast in YOUR neighborhood for the #Eclipse2017 @SteveGlazier breaks it down along the path… https://t.co/UmjfdhOiFZ

20 August by WeatherNation

Don't have your #Eclipse2017 glasses? There's other creative ways to view the #greatamericaneclipse @GarofaloWX has… https://t.co/WVx6vhGkFk

20 August by WeatherNation

Meteorologists @SteveGlazier & @GarofaloWX talk with our live reporter @JVPStorm who's in the path of totality and… https://t.co/ZDD2fwZJ9C

20 August by WeatherNation

Hail up to the size of a golf ball reported in parts of Ohio on Saturday. Check out some of the reports ->… https://t.co/49D9OA0s2t

20 August by WeatherNation

Flash flooding could be an issue in southern New Mexico this weekend. We are watching that region very closely. https://t.co/RoK3AypihP

19 August by WeatherNation

How's this for a spot to catch the total solar eclipse? #OregonCoast https://t.co/6yM7pFKZ7x

19 August by WeatherNation

RT @GarofaloWX: Hail/damaging winds continue to be a threat for parts of Ohio & Pennsylvania. @SteveGlazier, @NickMerianos, & I have more o…

19 August by WeatherNation

Here's a look at the cloud/visibility forecast for Monday's #Eclipse We'll post updates if anything major changes! https://t.co/NNC2TiePqG

19 August by WeatherNation

JUST IN: Severe T-Storm Watch issued for PA and eastern OH until 9pm EDT. https://t.co/QefgZXF5K5

19 August by WeatherNation

Storm survey by @NWSSiouxFalls concludes several tornadoes touched down in SW MN Friday eve. #MNwx #IAwx READ:… https://t.co/tRebKIxkv5

19 August by WeatherNation
Follow Us