National Oceanic and
Atmospheric Administration
United States Department of Commerce


FY 2015

A Tsunami Forecast Model for Nantucket, Massachusetts

Spillane, M.C.

NOAA OAR Special Report, PMEL Tsunami Forecast Series: Vol. 8, 118 pp, doi: 10.7289/V5MS3QPD (2015)

Operational tsunami forecasting by NOAA’s Tsunami Warning Centers relies on the detection of tsunami wave trains in the open ocean, inversion of these data (telemetered via satellite) to quantify their source characteristics, and real-time modeling of the impact on threatened coastal communities. For each such community, the latter phase of the process involves a pre-tested forecast model capable of predicting the impact, in terms of inundation and dangerous inshore currents, with sufficient resolution and within the time constraints appropriate to an emergency response. To achieve this goal, considerable advance effort is required to tune each forecast model to the specific bathymetry and topography, both natural and manmade, of the impact area, and to validate the model’s performance with a broad set of tsunami sources. Where possible, the validation runs should replicate observed responses to historical events, but the sparse instrumental record of these rare but occasionally devastating occurrences dictates that comprehensive testing also include a suite of scenarios that represent potential future events.

During the forecast model design phase, and in research mode outside the pressures of an emergency situation, more detailed and slower-running models can be investigated. Such a model, referred to as a reference model, represents the most credible numerical representation of tsunami response for a study region, using the most detailed bathymetry available and without the run-time constraint of operational use. Once a reference model has been developed, the process of forecast model design is to determine where efficiencies can be gained by reducing the grid resolution and increasing the model time step, while still adequately representing the salient features of the full solution.

This report documents the reference and forecast model development for Nantucket, Massachusetts. South of Cape Cod and east of Martha’s Vineyard, the name Nantucket applies to the county, the island, and the community upon it. The harbor opens to the north and the shallow Nantucket Sound; the east and south coasts are exposed to the North Atlantic and can be impacted by the passage of hurricanes and tropical storms. A similar pattern of exposure applies to tsunamis and, although there are no reports of tsunami impact to date, this report will document that the island is not immune should a significant earthquake occur, in particular one centered north of Puerto Rico. The population of Nantucket expands greatly with vacationers in the summer months. While the hazard associated with tsunamis is of low probability, the drastic impact of such events demonstrated around the globe in recent years has illustrated the need for emergency preparedness. This report addresses the tsunami aspects of the natural hazard spectrum.

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