NASA Demonstrates Tsunami Prediction System

WASHINGTON -- A NASA-led research team has successfully demonstrated for the first time elements of a prototype tsunami prediction system that quickly and accurately assesses large earthquakes and estimates the size of resulting tsunamis.

After the magnitude 8.8 Chilean earthquake on Feb. 27, a team led by
Y. Tony Song of NASA's Jet Propulsion Laboratory in Pasadena, Calif.,
used real-time data from the agency's Global Differential GPS (GDGPS)
network to successfully predict the size of the resulting tsunami.
The network, managed by JPL, combines global and regional real-time
data from hundreds of GPS sites and estimates their positions every
second. It can detect ground motions as small as a few centimeters.

"This successful test demonstrates that coastal GPS systems can
effectively be used to predict the size of tsunamis," said Song.
"This could allow responsible agencies to issue better warnings that
can save lives and reduce false alarms that can unnecessarily disturb
the lives of coastal residents."

Song's team concluded that the Chilean earthquake, the fifth largest
ever recorded by instruments, would generate a moderate, or local,
tsunami unlikely to cause significant destruction in the Pacific. The
tsunami's effect was relatively small outside of Chile.

Song's GPS-based prediction was later confirmed using sea surface
height measurements from the joint NASA/French Space Agency Jason-1
and Jason-2 altimetry satellites. This work was partially carried out
by researchers at Ohio State University, Columbus.

"The value of coordinated real-time observations from precision GPS,
satellite altimetry and advanced Earth models has been demonstrated,"
said John LaBrecque, manager of the Solid Earth and Natural Hazards
program in the Earth Science Division of NASA's Science Mission
Directorate in Washington.

Song's prediction method, published in 2007, estimates the energy an
undersea earthquake transfers to the ocean to generate a tsunami. It
relies on data from coastal GPS stations near an epicenter, along
with information about the local continental slope. The continental
slope is the descent of the ocean floor from the edge of the
continental shelf to the ocean bottom.

Conventional tsunami warning systems rely on estimates of an
earthquake's location, depth and magnitude to determine whether a
large tsunami may be generated. However, history has shown earthquake
magnitude is not a reliable indicator of tsunami size. Previous
tsunami models presume a tsunami's power is determined by how much
the seafloor is displaced vertically. Song's theory says horizontal
motions of a faulting continental slope also contribute to a
tsunami's power by transferring kinetic energy to the ocean.

The theory is further substantiated in a recently accepted research
paper by Song and co-author Shin-Chan Han of NASA's Goddard Space
Flight Center, Greenbelt, Md. That study used data from the
NASA/German Aerospace Center Gravity Recovery and Climate Experiment
(GRACE) satellites to examine the 2004 Indian Ocean tsunami.

When the Feb. 27 earthquake struck, its ground motion was captured by
the NASA GDGPS network's station in Santiago, Chile, about 146 miles
from the earthquake's epicenter. These data were made available to
Song within minutes of the earthquake, enabling him to derive the
seafloor motions.

Based on these GPS data, Song calculated the tsunami's source energy,
ranking it as moderate: a 4.8 on the system's 10-point scale (10
being most destructive). His conclusion was based on the fact that
the ground motion detected by GPS indicated the slip of the fault
transferred fairly little kinetic energy to the ocean.

"We were fortunate to have a station sufficiently close to the
epicenter," said Yoaz Bar-Sever, JPL manager of the GDGPS system.
"Broad international collaboration is required to densify the GPS
tracking network so that it adequately covers all the fault zones
that can give rise to large earthquakes around the world."

For information about NASA and agency programs, visit:

http://www.nasa.gov

Source: NASA