Simulation-Based Probabilistic Tsunami Hazard Analysis for Near-Field Seismic Sources: Application To the Tohoku Region, Japan.


Abstract eng:
Probabilistic tsunami hazard analysis is the fundamental prerequisite for rigorous risk assessment and thus for decisionmaking regarding mitigation strategies. The analysis involves numerous uncertain parameters that are related to geophysical processes (e.g. slip rate, slip distribution, and dip), potential sea conditions (e.g. tidal level), and inundation processes (e.g. roughness and topography). A comprehensive treatment of these uncertainties is challenging due to the lack of highresolution/accuracy data and the great computational effort involved in tsunami simulation. A simulation-based procedure to estimate the likelihood that tsunami inundation at particular location will exceed a given level, within a certain period of time, is presented. Key features of existing hazard assessment methodologies, such as worst-case scenario, sensitivity analysis, and probabilistic hazard analysis, are combined to develop a new procedure for probabilistic tsunami hazard assessment for near-field seismic sources. To reduce the computational efforts and to focus on the methodological aspect, only a specific seismogenic context, i.e. near-field sources in the Tohoku region of Japan, is taken into account. Nevertheless, the procedure can be extended to consider all possible sources of interest for the Tohoku region and can be applied to other subduction zones. Furthermore, only geophysical uncertainty is considered herein; notwithstanding such limitations, the simulation-based procedure facilitates the implementation of all other sources of uncertainties in a straightforward manner. After the selection of a tsunami occurrence model, the first step of the procedure is the definition of a magnitudefrequency distribution of major tsunami events; this function is then used to calculate the annual rate of exceedance of major tsunami events. For a given value of earthquake magnitude, size and geometry of the rupture area are determined using new empirical scaling relationships, bespoke for subduction areas. In this step, both aleatory and epistemic uncertainties of model parameters (i.e. position, length, width, strike, and dip) can be incorporated based on the probabilistic information available in the literature. In particular, multiple realizations of possible earthquake slip distributions are generated using a spectral synthesis method. The incorporation of the stochastic slip models in probabilistic tsunami hazard analysis is novel with respect to the previous studies; conventionally, slip distributions within a fault rupture plane are considered as uniform or randomly distributed (without realistic spatial distribution of the slip). Subsequently, for each generated slip distribution, the seafloor vertical displacement is calculated using analytical formulae and tsunami simulation is performed by solving nonlinear shallow water equations. By repeating the above procedure for numerous tsunami scenarios, the empirical distribution of the maximum wave heights and velocities (i.e. intensity measures) can be obtained for rigorous tsunami hazard analysis. The minimum number of simulations required to obtain stable estimates of tsunami intensity measures, especially the higher percentiles, is investigated through a statistical bootstrap analysis. The site-specific tsunami hazard curve can be derived by integrating the annual occurrence rates of the tsunami events and their tsunami inundation results. The results are particularly useful for tsunami hazard mapping purposes and the developed framework can be further extended to probabilistic tsunami risk analysis using tsunami fragility models.

Contributors:
Conference Title:
Conference Title:
16th World Conference on Earthquake Engineering
Conference Venue:
Santiago (CL)
Conference Dates:
2017-01-09 / 2017-01-13
Rights:
Text je chráněný podle autorského zákona č. 121/2000 Sb.



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 Record created 2017-01-18, last modified 2017-01-18


Original version of the author's contribution as presented on USB, paper 386.:
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