FAQ Results

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1. Does the MOST model use nested grids?
   
   The MOST (Method of Splitting Tsunami) model uses nested computational grids to telescope down into the high-resolution area of interest. Nested grids are used to have a minimum number of nodes in a wavelength in order to resolve the wave with minimum error.

   Relatively coarse grids are able to resolve the wave in deep water because its wavelength is long and fewer node points are needed. As the wave travels into shallow waters, the wavelength shortens (and the amplitude rises), requiring more node points, and thereby requiring high-resolution grids.

   For more Information:

   • Tsunami Inundation mapping
   • Tsunami Modeling and Forecasting
   
   
   Authority: NOAA Center for Tsunami Research
   
   
2. What are the input parameters for the MOST model of tsunami propagation and run-up and how does that support warning and forecasting?
   
   The input parameters for the MOST (Method of Splitting Tsunami) model can be set in several ways that depend on the application. The location and magnitude of the earthquake are used in a ground deformation model to estimate the vertical displacement of the ocean floor. This displacement is set to the initial displacement of the sea surface, which is then the initial condition for the tsunami wave in the MOST model. This is how it is run in a research mode. A set of earthquakes is used in doing a tsunami risk assessment for communities, including the maximum credible event for designing evacuation strategies.

   Operationally during a possible tsunami event, a sequence of different MOST simulations is run (more exactly: scaled from a pre-computed database of MOST model runs) as new information about the earthquake and tsunami become available. The first set is obtained from the earthquake alone. This process has been incorporated into the first version of the SIFT tsunami forecasting system that is being delivered to the U.S. Tsunami Warning Centers this Spring.

   Once actual observations of the tsunami become available at DART buoy stations, the tsunami source (and hence the earthquake parameters) are adjusted to match the observed tsunami. These new parameters are then used to make updated coastal tsunami forecasts for potential impact sites. This system under development will include the capability to run standby inundation models (SIMs, essentially high-resolution MOST models optimized for computation speed) for selected coastal communities, in order to get the best quality forecasts at those sites. This new version of SIFT will be delivered to the Warning Centers within a year from now.

   
   
   Authority: Dr. Hal Mofjeld, NCTR, May 3, 2006, NOAA Center for Tsunami Research
   
   References and more info:
   • Examples of the use of the MOST Model
   • Development of a realtime Tsunami Forecasting System (PDF)