[S-CG46] Uncovering stress accumulation and fault strengthening of megathrust earthquakes

[SCG46-02] Stress estimation on the Japan Trench Plate Boundary Fault 13 years after the 2011 Tohoku-oki Earthquake

★Invited Papers

*Marianne Conin¹, Kaitlin Schaible², Patrick Fulton³, Shuichi Kodaira⁴, Srisharan Shreedharan⁵, Mai-Linh Doan⁶, Hiroki Sone⁷, Christine Regalla⁸, Jamie Kirkpatrick⁹, Kohtaro Ujiie¹⁰, Weiren Lin¹³, Pei Pei⁶, Uisdean Nicholson¹¹, Maria-Jose Jurado¹², Lena Maeda⁴, Natsumi Okutsu⁴, Sean Toczko⁴, Nobu Eguchi⁴ (1.GeoRessources lab / University of Lorraine, 2.University of Texas / Institute for Geophysics, 3.Cornell University USA, 4.Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 5.Utah State University / Geosciences, 6.ISTerre / Universite Grenoble Alpes, 7.University of Wisconsin-Madison / Civil and Environmental Engineering, 8.Northern Arizona University / School of Earth and Sustainability, 9.University of Nevada, Reno / Geological Sciences and Engineering, 10.University of Tsukuba / Graduate School of Science and Technology, 11.Heriot-Watt University / Institute of GeoEnergy Engineering, 12.CSIC / Geosciences Barcelona, 13.Kyoto University / Graduate School of Engineering)

Keywords:IODP, JTRACK, stress evolution with time, fault strength, seismic cycle

In 2012, the International Ocean Discovery Program (IODP) exp. 343 JFAST successfully drilled the plate boundary fault zone that ruptured during the Mw9.1 Tohoku-oki earthquake, and recorded the stress state in the upper plate 11 months after the megathrust rupture. Results revealed a stress regime in favor of normal faulting, indicating a near total stress drop in this specific zone that recorded 50 m of slip (Lin et al., 2013; Brodsky et al., 2017). 12 years after JFAST, the IODP Expedition 405 (JTRACK) successfully re drilled the plate boundary at the same site, providing an unprecedented evaluation of stress evolution with time after a megaquake. New measurements reveal that the stress state is still in a low deviatoric stress and in a normal faulting regime and show evidence of aseismic slip on the fault, despite the ongoing plate convergence. Along strike observations of reverse faulting aftershocks indicate variability in stress and strength recovery in the margin. Together those results suggest this portion of the fault experiences low secular loading or is within a stress shadow of a locked patch, while it supports low stress.