P-16

Region Dividing Method to Clarify Frictional Properties in Plate Subduction Zone with Adjoint Data Assimilation

A. Suzuki (1), M. Kano (2), H. Nagao (1, 2), F. Komaki (1, 3)

(1) Graduate School of Information Science and Technology, The University of Tokyo
(2) Earthquake Research Institute, The University of Tokyo
(3) RIKEN Brain Science Institute

"Afterslip" is a slow slip event on a fault, which is often continuously observed for several months or years after an earthquake. Previous studies showed that an afterslip triggered by a large earthquake slowly propagates from the fault, and may cause a next large earthquake [e.g. Uchida et al.(2009)]. Frictional properties at a plate boundary are considered to control the time evolution of afterslips, so that the spatial distribution of frictional parameters is a key issue for prediction of states in the Earth's crust, i.e., "terra forecasting". Kano et al. (2013) applied an adjoint data assimilation to GNSS data in the case of the 2003 Tokachi-oki earthquake, and successfully reproduced the spatiotemporal distribution of the subsequent afterslip simultaneously estimating the frictional parameters. The simulation model consists of the frictional constitutive law and the quasi-dynamic equation of motion, both of which involve three frictional parameters a, a-b and L.

In order to obtain a realistic time evolution of afterslip, an appropriate assumption is required for the spatial pattern of frictional properties, although the previous studies a priori assumed the spatial pattern in heuristic ways. In this study, we propose a region dividing method using k-means to clarify the large-scale spatial structure of frictional properties in an afterslip region.