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

NEW: Fire weather alerts have been extended in California through the weekend. Story here: https://t.co/BwsVtremsF https://t.co/pcfDPXO4Pc

45 minutes ago by WeatherNation

MINNESOTA SNOWGLOBE - Take a look at this winter wonderland Thursday at White Bear Lake! #mnwx https://t.co/cYelRVnkrT

1 hour ago by WeatherNation

The time around Christmas looks like it will be colder than average for much of the country and potentially wetter.… https://t.co/FuDnoB9oKv

4 hours ago by WeatherNation

https://t.co/7u4oxasPks The stretch of beautiful weather in the northwest is about to end. But some good things will happen.

6 hours ago by WeatherNation

Wow. Unbelievable footage shows birds flying away from intense flames seen near Summerland, California as the… https://t.co/W8kMLwslgO

6 hours ago by WeatherNation

A view of the devastating California fires from NASA - https://t.co/8du0ZrlNQ1 https://t.co/oAj5HS56Aw

6 hours ago by WeatherNation

Gifting someone a @RokuPlayer this holiday season? Make sure they watch us on @WeatherNation. 📺❄️☀️🌧️ https://t.co/PRGk7rjxnF

7 hours ago by WeatherNation

DRIVE CAREFULLY - Check out this video from Cleveland, Ohio earlier on Thursday. Snow shower chances continue into… https://t.co/n3Su8X7NEX

8 hours ago by WeatherNation

The next generation of polar orbiting satellites, specializing in water cycles (floods, droughts, precipitation) an… https://t.co/2bAz70HMP4

8 hours ago by WeatherNation

Sad news today out of California from the #ThomasFire. https://t.co/xe7mTqxBV2

9 hours ago by WeatherNation

❄️🐕Do you get as excited as Luna for the #snow? https://t.co/F991fuMYAA

10 hours ago by WeatherNation

⛷️⛷️LEARNING TO SKI: Several of our @WeatherNation meteorologists took to the slopes for the first time at… https://t.co/eTOgBXk3BJ

12 hours ago by WeatherNation

Here is a look at today's high temperature forecast with @MeteorologistPC #Weather #WeatherNation #USA https://t.co/Y1tTC0YFre

12 hours ago by WeatherNation

Adapting and improving buildings to reduce structural risk from hurricanes: https://t.co/yxdT5e6nBl https://t.co/VijmJ1ipSI

13 hours ago by WeatherNation

FOUND IT! Denver's been asking, where's the #snow? ❄️❓❄️❓ A quick bout before dawn brought enough to break a 64 day… https://t.co/jaT4IxHGP4

14 hours ago by WeatherNation

Favorable wildfire conditons in the forecast for California the next few days. https://t.co/indg9eY2iA #CAwx #wildfires

14 hours ago by WeatherNation

Here are some of the big weather stories we are covering today on @WeatherNation https://t.co/7CnT8Cjyr6

16 hours ago by WeatherNation

More than 750 schools are closed near Detroit after a half a foot of #snow. ❄️ Hooray for a #snowday! ☃️ https://t.co/sX1JXxu4te

16 hours ago by WeatherNation
Follow Us