平成29（2017）年度　一般研究１実施報告書

課題番号	29−共研−1004	分野分類		統計数理研究所内分野分類		a
				主要研究分野分類		4
研究課題名	高解像度の地震活動確率予測モデルの開発
フリガナ 代表者氏名	ジュアン ジャンカン 庄 建倉		ローマ字		Zhuang Jiancang
所属機関	統計数理研究所
所属部局	モデリング研究系
職　　名	准教授

研究目的と成果（経過）の概要

We proposed the finite ETAS model, in which the fault geometry of a large earthquake is taken into account. We also extended the 2D epicentre ETAS model to a 3D hypocentre ETAS model to analyze earthquake hypocenters by introducing a beta distribution for modelling the earthquake depth. The 3D model provides the potential for forecasting seismicity with high resolution.

The finite-source ETAS model is applied to analyze the Japan Meteorological Agency (JMA) catalog during 1964--2014. We take six great earthquakes with magnitudes >7.5 after 1980 as finite sources and reconstruct the aftershock productivity patterns on each rupture surface. Comparing results from the point-source ETAS model, we find the following: (1) the finite-source model improves the data fitting; (2) direct aftershock productivity is
heterogeneous on the rupture plane; (3) the triggering abilities of M5.4+ events are enhanced; (4) the background rate is higher in the off-fault region and lower in the on-fault region for the Tohoku earthquake, while high probabilities of direct aftershocks distribute all over the source region in the modified model; (5) the triggering abilities of five main shocks become 2~6 times higher after taking the rupture geometries into consideration; and (6) the trends of the cumulative background rate are similar in both models, indicating the same levels of detection ability for seismicity anomalies. Moreover, correlations between aftershock productivity and slip distributions imply that aftershocks within rupture faults are adjustments to coseismic stress changes due to slip heterogeneity.

The 3D-hypocenter ETAS model is application to the JMA catalog for events above magnitude M4.0 in the Kanto region. We also studied the changes of seismicity patterns before and after the 2011 Tohoku earthquake.
The direct aftershocks of events from the post-Tohoku period are more diffusive in times and epicenters, but more concentrated in depths. The seismicity rate increased significantly following the Tohoku earthquake, especially along the interface of the subducting Pacific plate. The curve of cumulative background probabilities for events above M4.0 implies that the background rate decays back to the pre-Tohoku level in about 5 years after the Tohoku earthquake. However, the occurrence rates of smaller events (from M2.0 to M4.0) indicate that the adjustments of local stress field continue at finer scales.
Finally, we verify that the 3D model can reproduce the focal depths better than the 2D model and improves the forecasting performance.

当該研究に関する情報源（論文発表、学会発表、プレプリント、ホームページ等）

論文発表
1. Guo, Y., Zhuang, J., Hirata, N. and Zhou, S. (2017). Heterogeneity of direct aftershock productivity of the main shock rupture, Journal of Geophysical Research: Solid Earth, Vol.122, Issue7, pp.5288-5305, doi:10.1002/2017JB014064, July 2017.

学会発表

2. Guo, Y.*, Hirata, N. and Zhuang, J. (2017). Modeling and forecasting seismicity in the Kanto region by using a 3D ETAS model, 2017 Fall Meeting of the Seismological Society of Japan, Kagoshima Prefectural Citizens Exchange Center, Kagoshima City, Japan, 26 October 2017. (Poster)

3. Guo, Y.*, Hirata, N. and Zhuang, J. (2017). Statistical characteristics of seismicity in the Kanto region detected by the 3D-ETAS model, JpGU-AGU Joint Meeting 2017, Tokyo Bay Makuhari Hall, Chiba City, Japan, 24 May 2017. (Oral)

研究会を開催した場合は、テーマ・日時・場所・参加者数を記入してください。

研究参加者一覧
氏名	所属機関
郭一村	東京大学