Geoscience Reference
In-Depth Information
Bathymetry and Coastal Topography Data
Because of the wavelength of tsunamis being very long relative to the depth (typically on
the order of several tens to hundreds of kilometers in deep water), tsunami propagation from
source area to coastlines is strongly affected by the ocean bathymetry and coastal topography
over which it travels. Therefore, inundation modeling requires integrated bathymetry data over
the entire ocean basin and coastal topographic data. Requirements for horizontal resolution
of bathymetric data are not constant and vary depending on depth. The General Bathymetric
Chart of the Oceans (GEBCO) group recommends grid spacing of no more than 1 arc-minute
(
≈
2 km) in a 4,000 m deep open ocean, 10 arc-second (
≈
300 m) in a 100 m deep continental
shelf, 3 arc-second (
≈
90 m) in 10 m deep near-shore waters, and even smaller resolutions for
modeling onshore run-up motions (Intergovernmental Oceanographic Commission and Inter-
national Hydrographic Organization, 2005).
These recommendations for bathymetric data resolution are largely being met for the
majority of the U.S. coastline. Gridded global bathymetry data with 30 arc-second (
≈
1 km)
resolution recently became available from GEBCO (http://www.gebco.net/), and data were
generated by the combination of ship depth soundings with interpolation between sounding
points guided by satellite-derived gravity data from radar altimetry (Sandwell and Smith, 2009).
High-resolution digital elevation models (DEMs) for U.S. coastal regions are being developed
by NOAA's NGDC (http://www.ngdc.noaa.gov/mgg/inundation/tsunami/inundation.html).
Coastal bathymetric, topographic, and shoreline data are combined and integrated to yield
the grid size ranging from 1/3 arc-second (~10 m) to 36 arc-seconds (~1 km) based on data
compiled from various data sources (e.g., NGDC, National Ocean Service (NOS), USGS, Federal
Emergency Management Agency (FEMA), U.S. Army Corps of Engineers (USACE), and other fed-
eral, state, and local government agencies, academic institutions, and private companies). These
DEMs were developed speciically to support tsunami modeling efforts with NOAA's numerical
code Method of Splitting Tsunami (MOST) operated at NOAA/Paciic Marine Environmental
Laboratory (PMEL) but are publicly available (http://www.ngdc.noaa.gov/mgg/inundation/
tsunami/inundation.html). Although efforts by GEBCO and NOAA/NGDC have accelerated the
development and access of precise bathymetric data, certain regions of the United States still
lack adequate data to perform inundation modeling. For example, in coastal Alaska, only 3 sets
of 1/3 arc-second data are currently available, whereas 16 sets are available for the Washington,
Oregon, and California coasts.
Hydrodynamic Computational Models
Hydrodynamic modeling of tsunami generation, propagation, and run-up is challeng-
ing because of its complexity and multi-scale nature. It is complex because it involves multi-
multi-
phase (water, air, solid) interactions in a three-dimensional domain where some hydrodynamic
complex because it involves multi-
s multi-
hydrodynamic
fundamentals (e.g., turbulence) remain unsolved. The starting point for all inundation models
The starting point for all inundation models
is the source and how the bottom motion, in the case of tectonic displacements at the sealoor,
