IRN Andes-FrenSZ webinar 12/11

November 12, 2025 | International Ocean Discovery Program (IODP) Expedition 405

► Pei Pei, ISTerre, France

“Hydraulic structure of the Tohoku subduction zone : Drilling provides insights into the 2011 tsunami earthquake ”
In 2011, the Tohoku subduction zone experienced a Mw 9.0 earthquake and a devastating tsunami, with co-seismic displacement exceeding 40 m at the trench. This study investigates the hydraulic structure of the plate boundary fault zone (PBFZ) using new data from IODP Expedition 405, which drilled through the fault several times between September and December 2024. Drilling and Logging While Drilling (LWD) data were analyzed to evaluate fluid exchange between the formation and the borehole. A high-resolution flow profile from Hole C0019H (2024) reveals a main inflow zone at the base of the PBFZ ( 823 mbsf, 2.3 m thick), forming an overpressurized interval with strong temperature anomalies. In contrast, Expedition 343 (Hole C0019B, 2012) showed no significant inflow at the same depth. Comparison between the two drilling periods indicates that pore pressure has evolved from a post-seismic dissipated state in 2012 to a reloading stage in 2024, evidencing active fluid migration along the Tohoku fault zone.

► Marianne Conin, Universite de Lorraine, France

“IODP JTRACK : tracking a tsunamigenic fault, and it’s temporal evolution 13 years after a mega-earthquake”