Predicting Tsunamis With Supercomputers

Collaborative research between Tohoku University and Fujitsu has produced a faster tsunami prediction model.

AsianScientist (Mar. 17, 2015) – Researchers have developed a supercomputer-driven tsunami model that can forecast 75 times faster than existing real-time methods. Their results have been published in Geophysical Research Letters.

The Great East Japan Earthquake far exceeded the scale of previously envisioned earthquakes, exposing an urgent need to improve methods of real-time estimation. The disaster also illustrated the need for information beyond wave height, such as the scope of flooding.

Researchers from Tohoku University and Fujitsu Laboratories have now developed a tsunami model that quickly predicts the extent of flooding from sea surface deformation, which is estimated based on observation data on the shape of the tsunami out at sea and on tectonic shifts onshore at the time of the earthquake.

Since 2014, the two institutions have collaborated on joint research projects for real-time tsunami forecasts and predictions. Currently used tsunami flood simulations are an important practical tool for disaster preparedness, producing flood-hazard maps and more. However, such simulations are computationally intensive, as it takes time to solve nonlinear equations. As a result, simulations have not typically been used for real-time analysis.

In the present study, the researchers investigated the feasibility of using their parallelized tsunami model for real-time flood analysis, making use of the computational power of the K computer to perform highly efficient parallel computations.

Using a wave-source model estimated from observation data collected from the tsunami caused by the Great East Japan Earthquake, the team conducted flood simulations to verify the technology. To reproduce the tsunami’s flood dynamics in detail, the team used high-resolution topographic data, modeling an approximate ten km area around the City of Sendai’s coastal districts with a resolution of five meters.

This testing showed that simulations of the general extent of flooding in the City of Sendai could be completed in two minutes. Performing the same computations on a workstation would take several days. Even including the time needed to analyze the tsunami wave source from the observation data, the time to provide basic flood predictions was estimated to be approximately ten minutes. This would have been sufficiently fast for the tsunami caused by the Great East Japan Earthquake, which took one hour to reach the City of Sendai.

In addition, the team was able to reproduce results actually seen from the tsunami caused by the Great East Japan Earthquake. For example, the embankment of the Sendai East Road was able to stop the tsunami, which then passed through passageways underneath it.

The researchers will apply their prediction model to hypothetical cases of a massive earthquake in the Nankai Trough, a large region from which earthquakes originate, to test its effectiveness. In doing so, it is hoped that precise and targeted tsunami forecasts will help local governments and businesses around seaports better prepare tsunami-response measures.

The article can be found at: Oishi et al. (2015) Near-Field Tsunami Inundation Forecast using the Parallel TUNAMI-N2 Model: Application to the 2011 Tohoku-Oki Earthquake Combined with Source Inversions.

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Source: Tohoku University.
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