Ziyi Huang, Jiin-Jen Lee


September 29, 2009 Samoa tsunami attacked Pago Pago Harbor, the major harbor in American Samoa. The original tsunami waves were greatly amplified when they propagated into the harbor, causing extensive inundations and thus fatalities and village damages. A frequency-based numerical model developed by Lee and Xing (2010) was utilized to investigate the mechanism of the amplification. The fundamental resonance mode of the harbor was identified as 18-minutes period based on the average water depth; the computed amplification factor, defined as the ratio of responded wave amplitude to incoming wave amplitude, was quite large on the fundamental mode at the interior of the harbor. Tidal gauge measurements of several other tsunami events in Pacific Ocean verified the simulation results and further corroborated the local response due to the topography and bathymetry of the harbor is responsible for the amplification of incoming waves. An unfounded speculation was discussed to interpret the distinguishing frequency distribution of wave spectral density in the Samoa tsunami event.


tsunami waves; American Samoa; Pago Pago Harbor; frequency-based model; fundamental resonance mode; local response; mode shape; near-field tsunami


Beavan, J., X. Wang, C. Holden, K. Wilson, W. Power, G. Prasetya, M. Bevis, and R. Kautoke. 2010. Near-simultaneous great earthquakes at Tonga megathrust and outer rise in September 2009, ature, 466, 959-963.

Berkhoff, J. C. W. 1972. Computation of combined refraction-diffraction, Proc. 13th Coastal Eng. Conf., ASCE, New York, 471-490.

Lay, T., C.J. Ammon, H. Kanamori, L. Rivera, K.D. Koper, and A.R. Hutko. 2010. The 2009 Samoa-Tonga great earthquake triggered doublet, ature, 466, 964-968.

Lee, J. J. and X. Xing. 2010. Computer modeling for harbor planning and design, Handbook of Coastal and Ocean Engineering, World Scientific, Singapore, Chapter 25, 699-722.

Okal, E.A., J. Borrero, and C. Chagué-Goff. 2011. Tsunamigenic predecessors to the 2009 Samoa earthquake, Earth-Science Reviews, 107, 128-140.

Okal, E.A., H. M. Fritz, C. E. Synolakis, J. C. Borrero, R. Weiss, P. J. Lynett, V. V. Titov, S. Foteinis, B. E. Jaffe, P. L.-F. Liu, and I. Chan. 2010. Field survey of the Samoa tsunami of 29 September 2009, Seismological Research Letters, 81(4), 577-591.

Richmond, B. M., M. Buckley, S. Etienne, C. Chagué-Goff, K. Clark, J. Goff, D. Dominey-Howes, and L. Strotz. 2011. Deposits, flow characteristics, and landscape change resulting from the September 2009 South Pacific tsunami in the Samoan islands, Earth-Science Reviews, 107, 38-51.

Roeber, V., Y. Yamazaki, and K. F. Cheung. 2010. Resonance and impact of the 2009 Samoa tsunami around Tutuila, American Samoa, Geophysical Research Letters, 37, L21604.

U.S. Geological Survey. 2009. Poster of the Samoa islands region earthquake of 29 September 2009 -magnitude 8.0, (

Full Text: PDF

Creative Commons License
This work is licensed under a Creative Commons Attribution 3.0 License.