Expedition 405 summary

hugely successful drilling operations, combined with postexpedition work to measure the mechanical, frictional, paleomagnetic, and hydrogeologic properties of the core samples and to constrain the history of past seismic slip at Site C0019, will provide an unprecedented opportunity to advance our understanding of shallow subduction systems.Outreach during the expedition leveraged and elevated the success of the operations by sharing the outcomes with a variety of domestic and international audiences, including scientists, students, educators, stakeholders, and the general public.Thanks to the efforts of a large group of onboard outreach officers and their onshore support, activities included ship-to-shore broadcast events; interviews with science party members and crew; the publication of videos, blogs, magazine articles, and social media posts; and development of formalized classroom lesson plans and materials. Plain language summaryInternational Ocean Discovery Program (IODP) Expedition 405 aimed to understand the physical, chemical, and fluid conditions that produced the 2011 Tohoku Japan earthquake and tsunami and to investigate whether any conditions have changed during the past decade that may indicate how the system is preparing for the next event.Two sites were investigated during the expedition: Site C0019, located ~6 km west of the trench, where boreholes were drilled that targeted the plate boundary interface and the surrounding rocks and sediment of the upper and lower plates, and Site C0026 on the Pacific plate, ~8 km east of the trench, which was chosen to investigate rock and sediment properties before they enter the plate boundary deformation zone.Geophysical measurements made within the boreholes and from core samples were successfully collected at both sites, and two temperature observatories were installed across the plate boundary at Site C0019 to monitor fluid conditions.These data provide unprecedented opportunity to investigate processes that lead to large magnitude earthquakes and tsunamis, not only in the Japan Trench but in similar tectonic settings worldwide.In addition, these expedition objectives and successes were communicated to a broad audience, including scientists, students, teachers, and the general public, through the efforts of several shipboard outreach officers.