Shallow slip amplification and enhanced tsunami hazard unravelled by dynamic simulations of mega-thrust earthquakes

• Published in: Scientific reports Vol. 6; no. 1; p. 35007
• Main Authors: Murphy, S., Scala, A., Herrero, A., Lorito, S., Festa, G., Trasatti, E., Tonini, R., Romano, F., Molinari, I., Nielsen, S.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 11-10-2016; Nature Publishing Group
• Subjects: 704/2151/508; 704/4111; Earthquakes; Humanities and Social Sciences; Mechanical stimuli; multidisciplinary; Probability distribution; Rupture; Science; Sciences of the Universe; Seismic activity; Shear stress; Stochastic models; Stochasticity; Tsunamis; Wave height; Weather hazards
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/srep35007

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.