81009861

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Coastal Earthquakes and Flooding : Living on the Edge in Christchurch (NZ) Tokyo and Osaka (Jp)

沿岸地震と洪水 : 刃物の端にある町クライストチャーチ、東京と大阪

Review of Graduate School of Maritime Sciences, Kobe University

14

31-39

神戸大学大学院海事科学研究科

2017

2017-07-13

The majority of cities and megalopolis lie on sea-shores and river estuaries for the strategic position they provide. If city planners and settlers, have often taken flood hazards in consideration, more pervasive hazards like earthquake and how they interact with the late quaternary geomorphology have only recently become a concern, especially because of the increasing reliance of our contemporary societies on subterranean lifeline infrastructures. The present contribution is articulated around the hypothesis that the most recent unconsolidated sediments deposited by fluvial processes are the most likely to experience ground deformation during and after an earthquake and that those affects will in turn impact inundations from land or from the sea such as tsunamis. It also links the work to the conceptual framework of multihazards and the necessity to investigate further those complex interactions. Using GIS analysis and 2D CFD, we investigated the role of earthquakes in modifying the geometry of land in Christchurch, how it made the March 2014 flood worse, and then exported the lessons learned in Christchurch to Tokyo, Kobe, Osaka in order to understand better the present structural vulnerabilities. As the contribution is constructed as a demonstration using different examples rather than a typical scientific publication, we have used examples at different scales to show that (1) Holocene waterways on coastal low-lying land and their floodplain are particularly at risk of land-movement and increased flooding; (2) Assets of countries like Japan are concentrated for a large majorities in those areas at risk; (3) Tsunamis water flood use waterways as Troyan horses to penetrate inland and therefore the vulnerability seen in (1) further increase the vulnerability to tsunamis.

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