Influence of Flow Velocity on Tsunami Loss Estimation

Jie Song,Raffaele De Risi,Katsuichiro Goda

doi:10.3390/geosciences7040114

Abstract

Inundation depth is commonly used as an intensity measure in tsunami fragility analysis. However, inundation depth cannot be taken as the sole representation of tsunami impact on structures, especially when structural damage is caused by hydrodynamic and debris impact forces that are mainly determined by flow velocity. To reflect the influence of flow velocity in addition to inundation depth in tsunami risk assessment, a tsunami loss estimation method that adopts both inundation depth and flow velocity (i.e., bivariate intensity measures) in evaluating tsunami damage is developed. To consider a wide range of possible tsunami inundation scenarios, Monte Carlo-based tsunami simulations are performed using stochastic earthquake slip distributions derived from a spectral synthesis method and probabilistic scaling relationships of earthquake source parameters. By focusing on Sendai (plain coast) and Onagawa (ria coast) in the Miyagi Prefecture of Japan in a case study, the stochastic tsunami loss is evaluated by total economic loss and its spatial distribution at different scales. The results indicate that tsunami loss prediction is highly sensitive to modelling resolution and inclusion of flow velocity for buildings located less than 1 km from the sea for Sendai and Onagawa of Miyagi Prefecture.

Highlights

The most recent devastating tsunami that struck the Tohoku region of Japan in 2011 caused a tremendous economic loss
The results indicated that tsunami loss is highly sensitive to the two considered digital elevation models (DEM) resolutions, with the coarser DEM of 50 m resolution overestimating for Sendai and underestimating for Onagawa
The probabilistic tsunami loss curves for the entire portfolio in Sendai shown in Figure 6a indicate that velocity is not important at a city scale

Summary

Introduction

The most recent devastating tsunami that struck the Tohoku region of Japan in 2011 caused a tremendous economic loss. The underestimated tsunami hazard for the coastal areas in Tohoku region prior to the event highlighted deep uncertainty and potential bias in some of the key assumptions in the assessment (e.g., the maximum largest earthquake in the offshore region of Tohoku). The uncertainty in hazard propagates in the risk assessment, being transformed into tsunami impact parameters (i.e., economic loss). Catastrophe risk assessment is essential for achieving effective risk management to deal with the low-probability high-consequence catastrophes in the global insurance–reinsurance system by transferring financial risks among stakeholders [1,2,3]. Tsunamis are one of the low-probability high-consequence natural disasters, and the improved accuracy of tsunami loss estimation can help insurance/re-insurance underwriters to better understand their exposure to catastrophe risks and is beneficial for profitable design of risk transfer instruments [4,5,6]

Methods

Results

Conclusion