TSUNAMI RESEARCH GROUP
The Kuril Islands Tsunami of November 2006.
Energy Flux Tool
Non-Linear Shallow Water (NLSW) numerical simulations
Description: Tsunami interactions with submarine
ridges and numerous seamounts located in the tsunami path were a larger source
of late arrival of tsunami energy. In some locations these new sources were more efficent
in delivering tsunami energy than the direct wave. Travel time for these amplified energy fluxes is longer than for
the direct wave. Understanding this temporal distribution is important
for an application to tsunami warning and prediction.
To investigate energy flux traveling towards Crescent City (CC) during the Kuril tsunami,
a 5 degree box enclosing CC is considered. The energy flowing into and out of
the box is calculated. The time dependent energy flux is averaged over the length of each boundary.
One important property of the energy flux then arises, while the wave height can
change sign, the energy flux of the progressive wave is always aligned with the direction
of wave front propagation. Thus the noisy behavior of the sea level is replaced by the steadier
behavior of the energy flux. As a tsunami hazard mitigation tool, we propose that along with the
sea level records (which are often quite noisy) an energy flux for prediction of the delayed
tsunami signals be used.
References:
Kowalik Z., J. Horrillo, W. Knight and Tom Logan (2007),
The Kuril Islands tsunami of November 2006. Part I: Impact at Crescent City by distant scattering.
Accepted, Journal of Geophysical Research.
(Download PDF file, size: 5.28MB)
Horrillo J., W. Knight and Z. Kowalik (2007), The Kuril Islands tsunami of November 2006. Part II: Impact at Crescent City by local enhancement. Accepted, Journal of Geophysical Research. (Download PDF file, size: 5.24MB)
LOCATION OF CRESCENT CITY BOX
Figure 1. The box around Crescent City is constructed as follows: The west boundary is located at 129oW, the north boundary at 44.5oN, the south boundary at 39.5oN and the east boundary is on land.
ENERGY FLUX THROUGH BOX FACES
Figure 2. Energy flux through the western (blue), northern (red) and southern (green) faces of a 5 degree box around Crescent City.
Note: The numerical results given in Figure 2 show two distinct pulses
of energy crossing the western face of the box towards Crescent City (CC). Within the second pulse,
two maxima occur separated by 20 minutes time interval.
Nearly the entire energy flux enters the box through the western face (blue line). Southern and
northern energy fluxes (green and red lines respectively) are small with respect to the western face.
It is interesting to see that there is very little reflected energy coming back across the faces of
the box. This means that most of the incident energy is dissipated by the near shore bottom friction.
ENERGY FLUX THROUGH WESTERN FACE
Figure 3. Energy flux through the western face of a 5 degree box around Crescent City. Blue line: regular bathymetry. Red line: upper panel, Hess Rise is removed from bathymetry; lower panel, Koko Guyot is removed from bathymetry.
Note: Energy flux through faces of the box around Crescent City (CC) can be easily
applied to pinpoint the source of the second wave packet. First we simply removed from the bathymetry
the Hess Rise (see Figure 1) by setting it to an average of the surrounding depth. Next, the
Koko Guyot was removed in the same manner. In Figure 3 the energy flux crossing the western face is
plotted; in the upper panel the Hess Rise is removed but the Koko Guyot stays unchanged and
in the lower panel the Koko Guyot has been removed while the Hess Rise remains unchanged.
For comparison the energy flux across the western face with regular bathymetry is also given
(blue line)
The absence of Koko Guyot resulted in a restructuring of the energy flux through the western face of the
box in such a way that the first maximum in the second wave group practically disappeared (lower panel).
The absence of the Hess Rise (second maximum upper panel) leads to energy amplification from the Koko Guyot
as the Hess Rise did not scatter any longer the energy send by Koko Guyot towards CC.
The immense influence of the Koko Guyot on tsunami signal scattering is due to its size and strong contrast
between shallow and deep waters. It rises from the depth of 4750 m to within 250 m of the ocean surface.
VIDEO/ANIMATION
Energy FLux Vectors.
By Bill Knight
Note: The movie clearly identify Koko Guyot as an important bathymetric feature:
1) Tsunami energy is trapped and later radiated out by this prominent feature.
2) Tsunami fronts now approaching from the west are more efficiently enhanced
by the Mendocino Escarpment.
(Download. GIF file size: 802KB)
Modified 16 October 2007. Website questions or comments to Juan J. Horrillo.