Tsunami-wave Elevation Frequency of Occurrence for the Hawaiian Islands

Tsunami-wave Elevation Frequency of Occurrence for the Hawaiian Islands PDF

Author: James Robert Houston

Publisher:

Published: 1977

Total Pages: 37

ISBN-13:

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An investigation was undertaken to establish frequency-of-occurrence curves for tsunami-wave elevations near the shoreline for the Hawaiian Islands. A hybrid finite element numerical model was used to supplement historical data in determining the ten largest tsunami elevations from 1837 to 1976 at locations along the coastline of the islands. The numerical model was verified by comparing tide gage recordings at various locations in the Hawaiian Islands during the 1960 and 1964 tsunamis with numerical model calculations. Frequency-of-occurrence curves were established using data from the ten largest tsunami-wave elevations along the Hawaiian coastline. Figures and the table presented in the report can be used to calculate tsunami elevations 200 ft shoreward of the coastline for frequencies of occurrence as high as 1-in-10 years for the entire coastline of the Hawaiian Islands (except the coast of the uninhabited U.S. Navy target island of Kahoolawe). Runup nearly equals tsunami elevation at the shoreline for some of the coastline of the islands, but not for areas where flooding is substantial. A recommendation is given for development of a method to calculate land flooding during a tsunami. (Author).

Tsunami Response of Barbers Point Harbor, Hawaii

Tsunami Response of Barbers Point Harbor, Hawaii PDF

Author: Paul D. Farrar

Publisher:

Published: 1982

Total Pages: 146

ISBN-13:

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This study determines the degree of susceptibility of the proposed Barbers Point Deep-draft Pearl Harbor on Oahu Island, Hawaii, to tsunami waves. A finite-difference numerical model was developed to simulate the action of long-period waves within the harbor. This model included the effects of bottom friction, lateral mixing of momentum, radiation losses to the outside ocean, and the flooding of surrounding land areas. A large number of cases were simulated, representing tsunami inputs that could be expected in the area. The resulting water elevations, land flooding, and water movement are presented. The response of the harbor to the many different wave cases was combined with a study of the frequency-of-occurrence statistics for different harbor response events. This was done both for infrequent large tsunamis and for more frequent small amplitude tsunamis. Conservative probability methods were used for all results. On the basis of the response modeling and probability studies, the following conclusions were reached: (a) the harbor does not amplify incident long-period waves, especially those with a period of around 800 sec., (b) this amplification is, however, much smaller than would be predicted by linear response models, such as that of Durham (1978), which neglects nonlinear effects, such as bottom friction, lateral mixing, and flooding, (c) the nature of the harbor response will depend on the character of the incident wave, and (d) the harbor location chosen is a good location for the mitigation of tsunami hazards. (Author).

A Numerical Study of the Tsunami Response of the Hawaiian Islands

A Numerical Study of the Tsunami Response of the Hawaiian Islands PDF

Author: Eddie N. Bernard

Publisher:

Published: 1976

Total Pages: 102

ISBN-13:

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The response of linearized long waves to the eight major Hawaiian Islands is investigated numerically using a mathematical model of the island system. A spline interpolation scheme is utilized to convert the actual soundings of the island bathymetry to a 5.5 km square grid closely approximating the topography of the islands. A time-marching, central difference, explicit scheme is used to evaluate the wave field by the linear, long wave, Eulerian equations of motion and continuity in Cartesian coordinates for a frictionless, homogeneous fluid. The condition of no normal flow is employed at the island shorelines and a localized interpolation technique is utilized at the outer boundary to simulate a free-flow boundary. Verification of the numerical procedure is accomplished by agreement with analytic solutions of steady-state problems involving wave interaction with geometric islands in both constant and variable depth cases. Island response is determined by using a generalized time sequence input with a stipulated spectrum in the tsunami frequency range. This input is time stepped through the model for a duration sufficient to establish a statistical equilibrium within the system. The shoreline hydrographs, which record the time history of water elevation around the islands, are Fourier analyzed to obtain spectra for each shoreline point. These spectra are divided by the input spectrum to obtain transfer functions which represent the relative response of the system to waves in the tsunami period range. Verification of the response analysis is judged in terms of the agreement with the analytic response of a variable depth geometric island to a set of tsunami period waves. A technique for determining the period cutoff of a particular model system is demonstrated by comparison of responses of the same model using coarse and fine grids. The response analysis methods are applied to the model of the Hawaiian Islands for the case of a tsunami originating in the Alaskan region. Transfer functions are shown in averaged and contoured form for the island system and each individual island. The model study reveals that the numerical technique is appropriate for the response study of the Hawaiian Islands, that there are at least nine characteristic periods in the tsunami range to which the islands respond, and that interinsular reflections generate areas of high energy concentrations.

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