NIWA’s tsunami research
NIWA's research into tsunami covers modelling, underwater earthquakes and landslides, post-disaster surveys and risk/loss assessment.
NIWA’s areas of research into tsunami are listed below
Scientists use computational models to simulate the effects of tsunami. Some models only look at propagation over the open ocean; others are able to simulate their arrival at the shore and inundation (flooding) of dry land by the tsunami. All models are based on the same underlying mathematical equations of fluid motion.
Usually, the ocean volume is divided up into a grid of points or elements and the fluid equations are solved at each of these points/elements. Models can differ in terms of simplifying assumptions made on the equations, the numerical techniques used to solve those equations and the grid used. NIWA’s scientists use two models: RiCOM and Gerris.
RiCOM is based on a triangular mesh, by varying the triangles size slightly with each one it can grade smoothly between different sizes.
Figure: RiCOM grid coloured according to depth. In deeper water larger triangles can be used. In shallower areas, especially those with complex coastline, the grid grades to smaller triangles for finer resolution. Solid colours in the figure indicate where the triangles are so fine that they blend together.
Gerris is based on a square grid that may be refined by subdividing any given square into 4 subsquares.
Figure: Animation of adaptive level of refinement of wave elevation. Dark red is 0.8 nautical miles, dark blue is 101 nautical miles.
A refined simulation of the 2011 Tohoku Tsunami has been run using Gerris, with both data and an animation available.
NIWA scientists are also engaged in better understanding the risk that undersea earthquakes and landslides could pose to New Zealand’s coastal communities.
Such events can cause tsunami, and NIWA scientists are collecting high-resolution images of the seabed and its underlying tectonic faults.
Teams of scientists, including NIWA researchers, undertake reconnaissance missions to areas affected by tsunami (and other hazards, e.g. tropical cyclones) to look at their effects. These surveys are used to collect the data which inform risk and loss assessment models, and refine models of how tsunami waves behave.
Risk and Loss assessment
Data collected from post-disaster surveys is fed into risk and loss assessment models: the more accurately costs can be calculated, the better the decisions around risk-reduction initiatives can be. Such information can also be used by areas at risk to help them better prepare for tsunami.
NIWA and GNS have developed RiskScape, a software tool which enables users to analyse the risks and impacts of a range of hazards, including tsunami.
In addition, it can be used to help refine computer models of how tsunami waves propagate and interact with coastal areas.