Detiding Tsunami Currents to Validate Velocities in Numerical Simulation Codes using Observations Near Hawaii from the 2011 Tohoku Tsunami

Abstract:

The ability to measure, predict, and compute tsunami flow velocities is of
importance in risk assessment and hazard mitigation. Until recently, few
direct measurements of tsunami velocities existed to compare with model
results. During the 11 March 2001 Tohoku Tsunami, 328 current meters were
were in place around the Hawaiian Islands, USA, that captured time series
of water velocity in 18 locations, in both harbors and deep channels, at
a series of depths. Arcos and LeVeque[1] compared these records against
numerical simulations performed using the GeoClaw numerical tsunami model
which is based on the depth-averaged shallow water equations. They confirmed
that GeoClaw can accurately predict velocities at nearshore locations, and
that tsunami current velocity is more spatially variable than wave form
or height and potentially more sensitive for model validation.

We present a new approach to detiding this sensitive current data. This
approach can be used separately on data at each depth of a current gauge.
When averaged across depths, the Geoclaw results in [1] are validated. Without
averaging, the results should be useful to researchers wishing to validate their
3D codes. These results can be downloaded from the project website below.

The approach decomposes the pre-tsunami component of the data into three parts:
a tidal component, a fast component (noise), and a slow component (not matched
by the harmonic analysis). Each part is extended to the time when the tsunami
is present and subtracted from the current data then to give the ''tsunami current''
that can be compared with 2D or 3D codes that do not model currents in the
pre-tsunami regime.

[1] "Validating Velocities in the GeoClaw Tsunami Model using Observations Near
Hawaii from the 2001 Tohoku Tsunami"
M.E.M. Arcos and Randall J. LeVeque
arXiv:1410.2884v1 [physics.geo-py], 10 Oct. 2014.

project website: http://faculty.washington.edu/lma3/research.html