QUICK EVALUATION OF RUNUP HEIGHT AND INUNDATION AREA FOR EARLY WARNING OF TSUNAMI

Abstract

A methodology combining the offshore tsunami calculated by using numerical reciprocal Green's function (RGF) and the runup flow field calculated by using an analytical Green's function (AGF) is proposed to quickly estimate a tsunami hazard.For a vulnerable city, the RGF is computed previously via linear shallow water equations over real bathymetry and the offshore tsunami can be obtained promptly once the initial rupture is known. A transformation from time to space is then applied to obtain an equivalent waveform. With an integral with the AGF, derived by Carrier et al. [2003] based on 1D fully nonlinear shallow water equations over a uniform constant slope, the runup flow field is calculated. Thus, besides saving computation time and reducing the memory requirement, the desired initial condition for the AGF can also be generate by RGF. In this approach, the max wave height and the inundation distance are estimated very quickly and can be applied to broadcast an early warning of tsunami.To verify the method, data obtained during the 2004 Indian Ocean Tsunami from Sri Lanka and Phuket, Thailand is applied. The offshore condition is first verified by comparing with the record at Maldives. The accuracy of RGF is also tested. Then, by taking the nearshore shelf slope as the constant bottom slope for the analytical solution, the max tsunami height agrees reasonably well with the in-situ measurement. Therefore, this method is a useful tool for tsunami early warning by quickly estimating if the max wave height is higher than the seawall or the breakwater. The max inundation distance calculated by the analytic integral solution also has reasonable agreement with the field survey, but the value from the in-situ investigation scatters widely, which suggests that the detailed local topography plays an important role. A different method for the determination of the bottom slope is also tested and the result shows that the slope should be based on the bathymetry nearshore.