FY 2008

Developing tsunami forecast inundation models for Hawaii: Procedures and testing

Tang, L., C.D. Chamberlin, and V.V. Titov

NOAA Tech. Memo. OAR PMEL-141, NTIS: PB2009-100620, 46 pp (2008)

This report describes the procedures and testing for developing tsunami forecast inundation models, named Stand-by Inundation Models (SIMs), for Hawaii, as components of NOAA's tsunami forecast and warning system. The activity included sensitivity studies of nearshore tsunami wave characteristics and inundations for ranges of model grid setups, resolutions, and parameters. The SIM covering Kahului, Maui, is used as an example for demonstration of the development process.

The Kahului SIM was validated with 11 historical tsunami water-level records at Kahului tide station. The accuracy of the maximum wave height computed by the SIM is greater than 80% when the observed maximum wave height is greater than 0.5 m, and 50% when the observation is between 0.3 to 0.5 m. The error of the modeled arrival time of the first peak is within ±3% of the travel time. Wavelet analyses indicate that the peak wave period at the station mainly falls into one of three harbor and local resonant periods, near 16, 24, or 34 min (±2 min). This is relevant to the geographic location of the tsunami source. The SIM outputs are also verified with numerical results from a reference inundation model (RIM) with a higher resolution of 1/3 arc-second (10 m). The optimized SIM can accurately provide a 4-hour forecast of first-wave arrival, amplitudes, and a reasonable inundation limit within minutes of receiving tsunami source information constrained by deep-ocean DART measurements. It is capable of reproducing later tsunami waves reflected or scattered by far-field bathymetry that may arrive hours after the first arrival. The Kahului SIM is tested against different scenarios of simulated T_Mw 7.5, 8.2, 8.7, and 9.3 tsunamis based on subduction zone earthquakes in the Pacific. It shows robust results for all test cases. The tsunami hazard assessment study for Kahului indicates that moment magnitude alone is inadequate to provide warning guidance for coastal communities, since it contains information relevant only to the source. The SIMs, which contain local bathymetric and topographic information, and utilize the dynamic boundary conditions from the propagation database, are particularly designed for site-specific forecasts for coastal communities. Only by combining DART-constrained tsunami magnitude with site-specific SIMs can the forecast completely cover the three distinct stages of earthquake-generated tsunamis—generation, deep-ocean propagation, and coastal transformation, including runup.