第22回統計地震学セミナー

日時(Time)

2011-11-25 / Friday (金曜日)　13:30〜14:30

場所(Location)

統計数理研究所 D312B室
(Room D312B @ Institute of Statistical Mathematics)

講演題目(Title)

The slip distribution of the 2011 Tohoku-oki earthquake inferred from the spatial distribution of its aftershocks

講演者
(Speaker)

岩田　貴樹（Iwata, Takaki）,
統計数理研究所　特任准教授

概要(Abstract)

We have developed a method to estimate the spatial slip distribution of a large earthquake based on its on-fault aftershock activity and the rate- and state-dependent friction model (Dieterich, 1994, JGR). This talk will represents the application of this method to the 2011 Tohoku-oki earthquake. The outline of the method is as follows. First, we divided the source area of the destructive earthquake into 450 subfaults of which size is 20 x 20 km. Next the slips of each subfault were optimized to make the expected spatial distribution of aftershocks fit to the observed distribution during one day after the mainshock. The expected distribution was derived from the Dieterich’s formulation and the goodness-of-fit between the expected and observed distributions was evaluated by means of the likelihood for point-process model. Then we constructed a Bayesian model incorporating smoothness constraint on the spatial slip distribution, because optimizing such a huge number of parameters is unstable; the incorporation of the constraint enhances the stability of the optimization. To compute the posterior distribution of the parameters in this Bayesian framework, the Markov Chain Monte Carlo method was used. The result of this approach found an asperity close to the hypocenter and some small asperities located to the southwest of the hypocenter. This feature is consistent with the results of some slip inversions based on seismograph, geodetic, and/or tsunami data, suggesting that seismic activity data would play an important role in the estimation of rupture process of an earthquake.