Stress accumulation in the Marmara Sea estimated through ground-motion simulations from dynamic rupture scenarios

We compare ground motions simulated from dynamic rupture scenarios, for the seismic gap along the North Anatolian Fault under the Marmara Sea Turkey), to estimates from empirical ground motion prediction equations (GMPEs). Ground motions are simulated using a finite difference method and a 3D model of the local crustal structure. They are analyzed at more than a thousand locations in terms of horizontal peak ground velocity. Characteristics of probable earthquake scenarios are strongly dependent on the hypothesized level of accumulated stress, in terms of a normalized stress parameter T (Aochi and Ulrich, 2015). With respect to the GMPEs, it is found that simulations for many scenarios systematically overestimate the ground motions at all distances. Simulations for only some scenarios, corresponding to moderate stress accumulation, match the estimates from the GMPEs. The difference between the simulations and the GMPEs is used to quantify the relative probabilities of each scenario and, therefore, to revise the probability of the stress field. A magnitude Mw7+ operating at moderate prestress field (0.6 < T ≤ 0.7) is statistically more probable, as previously assumed in the logic tree of probabilistic assessment of rupture scenarios. This approach of revising the mechanical hypothesis by means of comparison to an empirical statistical model (e.g. a GMPE) is useful not only for practical seismic hazard assessments but also to understand crustal dynamics.