FY 2006

Assessment of potential tsunami impact for Pearl Harbor, Hawaii

Tang, L., C. Chamberlin, E. Tolkova, M. Spillane, V.V. Titov, E.N. Bernard, and H.O. Mofjeld

NOAA Tech. Memo. OAR PMEL-131, NTIS: PB2007-100617, 36 pp (2006)

A 1/3 arc-second (10 m) high-resolution tsunami inundation model utilizing the 2D MOST model was developed for Pearl Harbor, Hawaii. The present study focuses on validating the model with historical tsunami water level records, identifying the worst-case scenario, and evaluating the potential impacts on Pearl Harbor. A secondary objective is to explore the effect of the changed Honolulu coastline on tsunami waves.

This study examined nine historical tsunamis, including four recent events with high quality measurements at DART buoys and tide gages, and five destructive tsunamis in Hawaiian history. The model tsunamis were in excellent agreement with the observations for the four recent events, as well as for the 1964 Alaska and 1946 Unimak tsunamis. The model also yielded reasonable comparisons for the 1952 Kamchatka, 1957 Andreanof, and 1960 Chile tsunamis. These comparisons provide validation references for the tsunami vulnerability study.

The NCTR's pre-computed propagation database provided the computed maximum wave amplitudes at a site offshore of Pearl Harbor from 804 synthetic tsunami sources around the Pacific Ocean. These data, combined with their directionalities, served as guidance for selecting 18 simulated 9.3 M_w tsunamis, one from each of the major subduction zones. An inundation test model with 1 arc-second (30 m) resolution was employed to quickly identify the worst-case scenario, which is then used in the high-resolution model. The comprehensive modeling results indicate that hazardous wave conditions are likely to be created in the study area by tsunamis originating from the Kamchatka, East Philippine, Japan, Alaska-Aleutian, South American, and Cascadia Subduction Zones. In particular, the Kamchatka scenario produces the most severe impact on the study site. The unit source NZKT B38, to the north of Tonga, has the maximum offshore amplitude from a single unit source.

Computed waveforms at 16 points in the study area were used to evaluate the potential impacts on Pearl Harbor. With a typical incident wave period of 24 min or less, the north shore of Ford Island experiences significantly smaller waves than the open coast. When the typical incident wave period reaches 48 min or more, a characteristic resonance with a period of around 96 min at Pearl Harbor is excited, resulting in similar maximum wave amplitudes both inside Pearl Harbor and on the open coast. Larger wave heights and higher velocities are found in the Entrance Channel, the West Loch, and the channel near Hospital Point. Model results show no inundation at the NOAA building site for any of the simulations, including the five historical destructive tsunamis and the worst-case scenario.

A 1960 digital elevation model based on historical nautical charts of the region was developed. Modeling results indicate that changes in the Honolulu coastline since 1940 have little effect on the waveforms in both Pearl Harbor and Honolulu Harbor.