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Institute of Marine Sciences, Physical Oceanography

TSUNAMI RESEARCH GROUP


The Kuril Islands Tsunami of November 2006.

Impact at Crescent City by distant scattering

Non-Linear Shallow Water (NLSW) numerical simulations

Description: The Global Tsunami Model (GTM) is applied to the tsunami of November 15, 2006 in the Northern Pacific with spatial resolution of one minute.
The tide gauge at Crescent City (CC) recorded an initial tsunami wave of about 20 cm amplitude and a second larger energy packet arriving two hours later. The first energy input into the CC harbor was the primary (direct wave on great circle) wave traveling over the deep waters of the North Pacific. Interactions with submarine ridges and numerous seamounts (ie. Emperor Chain) located in the tsunami path were a larger source of tsunami energy than the direct wave. Travel time for these amplified energy fluxes is longer than for the direct wave. Prime sources for the larger fluxes at CC are interactions with Koko Guyot and Hess Rise. Tsunami waves travel next over the Mendocino Escarpment where the tsunami energy flux is concentrated due to refraction and directed towards CC.
Local tsunami amplification over the shelf-break and shelf are important as well, Horrillo et al.(2007). In many locations along the North Pacific coast, the first arriving signal or forerunner, has lower amplitude than the main signal which often is delayed. Understanding this temporal distribution is important for an application to tsunami warning and prediction. 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)




Northern Pacific Bathymetry

Figure 1. One minute resolution bathymetry based on the GEBCO Atlas. The Figure Shows important bathymetric features within tsunami source and Crescent City .


Note: Bathymetric features as shown in figure are important in reorganizing and focusing tsunami signal towards Crescent City (CC). The tsunami signal interacts with the Emperor Seamount Chain particularly with the exceptionally large Koko Guyot. The tsunami is scattered into new directions and by interference of these batymetric features generates a new set of waves. A complicated packet of waves arrives at CC, with the first arrival preserving the properties of the initial wave generated in the Kuril Islands trench, and a second, larger wave group arriving about 2 hours later. Differences in the wave front direction show that the two waves travel different routes. While the first wave group arrives from the north-west via the great circle route and deep Aleutian trench, the second wave group arrives from the west. This latter wave is directed towards CC by secondary sources (ie. Koko Guyot and Hess Rise).




Figure 2. Maximum wave amplitude in the entire Pacific.


Note: The maximum amplitude distribution shows that the tsunami traveled over the entire Pacific. Some of the tsunami energy propagates in a finger-like pattern, a product of wave refraction and focusing around islands/seamounts/passages chain systems. Closer examinations show that the oceanic ridges and seamounts tend to refocus tsunami energy. Our interest is in energy concentration along the Mendocino Escarpment which is directed towards Crescent City.




Figure 3. Energy flux vectors 3.5 hours (upper panel) and 4 hours (lower panel) after tsunami onset. Note radially expanding wave front centered on Koko Guyot


Note: To further identify Koko Guyot as an important bathymetric feature, figure shows the energy flux vectors immediately following passage of the main energy lobe past Koko. Note the new wave front radiating from this secondary source. The Hess Rise is an elongated plateau, located to the east from Koko Guyot, with a few smaller subdomains which generally parallel the Mendocino Escarpment. The Hess Rise ridge like structure tends to enhance tsunami scattered from Koko Guyot and directs it towards Mendocino Escarpment.




MENDOCINO ESCARPMENT

Figure 4. Numerical experiment of three waves traveling parallel to the Mendocino Escarpment. Amplitude given by colors. Vectors denote energy flux.


Note: The strongest amplification occurs along the escarpment shallow part due to the continuously wave refraction. The direction of wave propagation (coming from the West) seems to play the major role in tsunami enhancement along the Mendocino Escarpment.




VIDEO/ANIMATION

a) Wave propagation (plan view)

Note: Notice duration of tsunami ringing on Emperor Seamount Chain specially on Koko Guyot. (Download high resolution version. MOV file size: 81.2MB)




b) Wave propagation (East view)

Note: Notice wave refraction and higer tsunami energy along the shallow part of Mendocino Escarpment. (Download high resolution version. MOV file size: 78.8MB)




c) Maximum wave height propagation

Note: Notice tsunami energy concentration along Mendocino Escarpment.
Plotting maximum wave height in time is convenient for visualizing the delay of the maximum wave. As it can be seen from the animation, arrival times of maximum amplitude in this location does not correspond to the first wave. The same fact is observed on Mexican coast where some late tsunami signals are coming from Hawaii. (Download high resolution version. MOV file size: 35.3MB)




Modified 4 October 2007. Website questions or comments to Juan J. Horrillo.