Pamela Grothe – Tsunami Digital Elevation Modeling

We build high resolution digital elevation
models for tsunami modeling. We try to gather any elevation data we can – that includes
bathymetric data and topographic data. Topographic data is elevation data of land and bathymetric
data is the elevation data for underneath the ocean surface. Because we cannot see that
because the ocean and the water we have to use other techniques to gather that elevation,
or what we call bathymetry, such as sonar from ships. So this image here: the darker
blue is going to represent the deeper parts of the ocean. So you can see as the blues
become lighter up we’re going shallower towards to coastline. Then as we hit the coastline
we switch colors to the greens and browns to represent the different elevations along
the coast. The Crescent City D.E.M. is interesting because there’s unique harbor dynamics for
Crescent City. Historical tsunamis have been worse in Crescent City than nearby areas partially
because the wave has been funneled with offshore topography, but also because when the wave
gets into the harbor of Crescent City, it kind of resonates off the breakwaters and
just historically its caused higher inundation and waves in that region. For the March 11
tsunami, it was great to actually have this D.E.M. that was already produced and used
for tsunami hazard preparedness because the tsunami was propagated across the whole Pacific
basin. By having this D.E.M. in advance we were able to use it in our model to predict
the high water line or how far this wave is going to inundate into the land so that we
can give out evacuations…so we know what areas need to be evacuated and not evacuated.
Crescent City has kind of got a bull’s-eye marked on it because it’s located 4,500
miles away from where the actual tsunami happened, but because of the Mendocino Fracture Ridge,
it funneled that tsunami wave energy straight towards Crescent City and on top of that because
of the dynamics of the harbor, the wave resonated and had like 8 feet of inundation from that
wave way across the Pacific Ocean.

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