Impact Forecasting’s Earthquake and Tsunami Model for Japan

The 2011 earthquake off the Pacific coast of Tōhoku, Japan was a magnitude 9.1 (Mw) undersea megathrust earthquake that occurred on Friday 11 March 2011. It was the most powerful earthquake ever recorded in Japan, and the fourth most powerful earthquake in the world since modern record-keeping began in 1900.

The earthquake triggered tremendous tsunami waves that reached heights of up to 40 meters and travelled up to 10 km inland. The earthquake was so powerful that it moved the Honshu island 2.4 m East. The resulting total damage was estimated to be about $210 billion USD with insured losses reaching $35 billion USD.

The 2011 Tohoku mega-thrust earthquake highlighted the need and importance to also consider the tsunami risks along with shake during earthquakes, which can help accurately account the potential impacts of such extreme events for risk management and risk transfer strategy.

Impact Forecasting Earthquake and Tsunami global team have spent almost two years in developing fully probabilistic catastrophe model which has a capability to model losses due to earthquake (ground-shaking) and induced tsunamis along the Japan coast in a probabilistic manner, and for historical scenarios.

The model incorporates the latest earthquake forecasts with time-dependent rupture probabilities and tsunamis are simulated through a fully hydrodynamic model that simulates all phases of tsunami (generation, propagation and inundation). A direct integration of tsunami events within the stochastic earthquake event set allows for more robust representation and seamless computation of combined earthquake shaking and tsunami losses in the Impact Forecasting’ loss modelling platform ELEMENTS.

Robust tsunami simulation through 2D hydrodynamic modelling (Delft3D by Deltares) is based on high resolution local elevation, bathymetry and tsunami defence data. Detailed land cover information is utilized to account for the variable ground frictions together with a superior inundation scheme to serve as a basis for the accurate modelling of tsunami inundation extents. Due to the high-resolution modelling and extensive number of simulated events, cloud computing was required.

Extensive sensitivity testing was performed during model development. For Tohoku event, four different earthquake source models were modelled, and individual results compared with survey observations collected by the 2011 Tohoku Earthquake Tsunami Joint Survey (TTJS) Group.

Impact Forecasting’s Earthquake and Tsunami model was validated through historical back-testing for client portfolios for numerous historical events between 2001-2016.