Abstract
The 2011 Tohoku earthquake produced an unexpected large amount of shallow slip greatly contributing to the ensuing tsunami. How frequent are such events? How can they be efficiently modelled for tsunami hazard? Stochastic slip models, which can be computed rapidly, are used to explore the natural slip variability; however, they generally do not deal specifically with shallow slip features. We study the systematic depth-dependence of slip along a thrust fault with a number of 2D dynamic simulations using stochastic shear stress distributions and a geometry based on the cross section of the Tohoku fault. We obtain a probability density for the slip distribution, which varies both with depth, earthquake size and whether the rupture breaks the surface. We propose a method to modify stochastic slip distributions according to this dynamically-derived probability distribution. This method may be efficiently applied to produce large numbers of heterogeneous slip distributions for probabilistic tsunami hazard analysis. Using numerous M9 earthquake scenarios, we demonstrate that incorporating the dynamically-derived probability distribution does enhance the conditional probability of exceedance of maximum estimated tsunami wave heights along the Japanese coast. This technique for integrating dynamic features in stochastic models can be extended to any subduction zone and faulting style.
Highlights
Ensemble, and is related to the phase spectrum of the slip distributions at large wavelengths
As we are interested in tsunamigenic earthquakes we firstly aim to extend the near uniform slip probability density function (SPDF) in the stochastic models to the surface in order to allow large slip near the Earth’s surface
We have introduced the concept of the SPDF and have highlighted the importance of accounting for its spatial variation when considering earthquake source models in SPTHA
Summary
Ensemble (see Methods for a description of how the SPDF is calculated), and is related to the phase spectrum of the slip distributions at large wavelengths. Studies where the phase of the lowest wavelengths are coherently constrained are generally focusing on the reproduction of particular past events (e.g. Tohoku[19,23]) This naturally leads to a concentration of the SPDF in the area of the designated asperity. We use a large ensemble of 2D dynamic simulations to investigate if a Tohoku like fault exhibits depth-dependent systematic deviations from a spatially uniform slip probability, only as a consequence of dynamic effects during the rupture. We test this hypothesis for large tsunamigenic earthquakes by comparing systematic features observed in the dynamic models with the SPDF generated using a generic stochastic model. We analyse the effect of this correction on the conditional probability of exceedance of maximum tsunami wave heights along the Tohoku coastline; the probability of exceedance that we consider is conditional to the occurrence of a M 9 earthquake
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