Development of an Integrated Numerical Framework for Tsunami Hazard Assessment at Nuclear Installations, 20-R8268
Principal Investigators
Debashis Basu
Kaushik Das
Ron Janetzke
John Stamatakos
Todd Mintz
Rob Sewell, Consultant
Inclusive Dates: 11/14/11 – 09/01/12
Background — Tsunamis are a series of long ocean waves generated by large-scale earthquakes or landslides that occur along active faults near continental margins or subduction zones. The primary aim of the ongoing work is to develop an integrated tsunami analysis method for risk assessment at nuclear installations. The analysis is primarily focused on earthquake-generated tsunamis. The developed method calculates parameters such as maximum wave runup height, impact velocity, and inundation area from an earthquake generated tsunami. The generation stage of tsunami evolution includes the formation of the initial disturbance of the ocean surface caused by earthquake-triggered deformation of the sea floor. Subsequently, this initial disturbance of the water surface evolves into a long gravity wave radiating from the earthquake source. Developing an integrated tsunami analysis method will include predicting the initial wave height that is linked to the earthquake source mechanisms.
Approach — This ongoing research has resulted in the development of an integrated computational methodology to simulate the generation, propagation, and impact of an earthquake-generated tsunami. Developing this integrated approach involved developing a tsunami source model that takes into account local geological and tectonic processes as well as observed seismic and geodetic (sea floor and land deformation) data. In addition, accurate and finely resolved bathymetric and topographic data were used to generate the far and near-field computational grids. After generating the grid, numerical simulations were carried out to model tsunami generation, propagation, and runup. Simulated results were compared to available field data and observations.
The tsunami waves were simulated using the fully nonlinear and dispersive Boussinesq wave model FUNWAVE-TVD. Appropriate methodology is being adopted based on existing literature to select the earthquake source to be used in the tsunami model. For the present work, three tsunamis will be studied and modeled. The first is the 2011 Tohoku-Oki tsunami that took place on March 11, 2011, from a magnitude 9.1 earthquake. Geophysical records of the earthquake and the resulting tsunami from seismometers, Global Positioning System receivers, tide gauges, ocean bottom pressure sensors and other instruments, as well as various other observations provide significant documentation of this tsunami.
Two tsunami cases are being studied for the United States, one for the east coast and another for the west coast. Bathymetric data were used to generate a topographic grid to simulate the wave propagation in the far field and near field. Both the tsunami far- and near-field coastal impacts will be analyzed. For the analysis of the near-field coastal impacts, the effect of the tsunami waves on the structures will be calculated, which will provide a more realistic estimate of damage from the wave and the impact of debris on the power plants and facilities. Finally, the proposed work will try to estimate structural damage (loss in dollars) caused by tsunami forces using the simulation results of tsunami inundation and geographic information system analysis of post-tsunami survey data. This will lead to a new quantitative understanding of the relationship between local damage and tsunami hazards. Presently, tsunami hazards are assessed either by analyzing historic data or by using shallow water wave solvers. The overall analysis also will include comparisons of the predictions with the observations.
Accomplishments — Project staff members have so far
obtained bathymetric data for the different sites, and have completed
FUNWAVE-TVD simulations for the Diablo Canyon site. The problem domain was
limited by the available bathymetry data (238.51 to 239.17 E longitude,
35.07 to 35.34 N latitude). The horizontal bathymetry resolution for this
simulation was 100 meters. The simulations revealed that FUNWAVE-TVD is able
to provide a realistic prediction of the wave propagation and the variation
of the wave height for the Diablo Canyon site. Project staff members have
also started simulations of the Diablo Canyon site using FLOW–3D. FLOW–3D is
a Navier Stokes solver and is primarily being used for the near-shore
region. One of the aims of this project is to compare FUNWAVE-TVD and
FLOW–3D for simulations of near-shore hydrodynamics. Project staff members
also evaluated different slip distribution inversions that provide the
information to calculate the complex sea floor patterns associated with
major earthquakes, which will be used as the initial condition for the
tsunami models. Two abstracts were submitted to the 23rd International Ocean
and Polar Engineering Conference (ISOPE–2013). Once the two abstracts are
accepted, full-length papers will be prepared.
