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Short historical and even shorter instrumental records limit our perspective of earthquake maximum magnitude and recurrence and thus are inadequate to fully characterize Earth’s complex and multiscale seismic behavior and its consequences. Motivated by the mission to fill the gap in long-term paleoseismic records of giant (Mw 9 class) subduction zone earthquakes, such as the Tohoku-Oki earthquake in 2011, International Ocean Discovery Program Expedition 386 successfully collected 29 giant piston cores at 15 sites (total core recovery = 831.19 m), recovering up to 37.82 m long, continuous upper Pleistocene to Holocene stratigraphic successions of 11 individual trench-fill basins that are expected to have recorded past earthquakes. Preliminary expedition results document event-stratigraphic successions comprising numerous event deposits and initially characterize their different types, facies, properties, composition, and frequency of occurrence, which show spatial variations across the entire Japan Trench. The occurrence of several tephra beds, radiolarian biostratigraphic events, and characteristic variations of paleomagnetic declination and inclination that probably represent paleomagnetic secular variation reveal high potential for establishing robust age models in all parts of the Japan Trench. The central Japan Trench models are most likely to cover the longest timescales, with expected age ranges reaching back to ~24 ka. Together, these preliminary initial results indicate that the applied concept and strategy of multisite coring will likely be successful to test and further develop sub-marine paleoseismology to extract megathrust earthquake signals from event-stratigraphic sequences preserved in the sedimentary record. Obtained data and samples will now be examined using postexpedition multimethod applications to comprehensively characterize and date event deposits. Detailed work will include detailed characterization of the sedimentologic, physical, and (bio-)geochemical features; stratigraphic expressions of relationships; and spatiotemporal distribution of event beds. These will be analyzed as foundational proxy evidence for distinguishing giant earthquakes from smaller earthquakes and aseismic processes driving mechanisms to ultimately develop a long-term record of giant earthquakes. Furthermore, Expedition 386 achievements comprise the first ever high temporal and high spatial resolution subsurface investigation and sampling in a hadal oceanic trench, which are the deepest and least explored environments on our planet. Preliminary initial results show high total organic carbon content and downcore pore water and headspace gas profiles with characteristic changes related to organic matter degradation. In combination, these are suggestive of the occurrence of intensive remineralization and reveal evidence of nonsteady-state behavior. Together with the successful offshore sampling for microbiology postexpedition analyses and research, this provides exciting new perspectives to advance our understanding of deep-sea elemental cycles and their influence on hadal environments. 

Short historical and even shorter instrumental records limit our perspective of earthquake maximum magnitude and recurrence and thus are inadequate to fully characterize Earth’s complex and multiscale seismic behavior and its consequences. Motivated by the mission to fill the gap in long-term paleoseismic records of giant (Mw 9 class) subduction zone earthquakes, such as the Tohoku-Oki earthquake in 2011, International Ocean Discovery Program Expedition 386 successfully collected 29 giant piston cores at 15 sites (total core recovery = 831.19 m), recovering up to 37.82 m long, continuous, upper Pleistocene to Holocene stratigraphic successions of 11 individual trench-fill basins that are expected to have recorded past earthquakes. Preliminary expedition results document event-stratigraphic successions comprising numerous event deposits and initially characterize their different types, facies, properties, composition, and frequency of occurrence, which show spatial variations across the southern, central, and northern Japan Trench. The occurrence of several tephra beds, radiolarian biostratigraphic events, and characteristic variations of paleomagnetic declination and inclination that probably represent paleomagnetic secular variation reveal high potential for establishing robust age models in all parts of the Japan Trench. The central Japan Trench models are most likely to cover the longest timescales, with expected age ranges reaching back to ~24 ka. Together, these preliminary initial results indicate that the applied concept and strategy of multisite coring will likely be successful to test and further develop submarine paleoseismology to extract megathrust earthquake signals from event-stratigraphic sequences preserved in the sedimentary record. Obtained data and samples will now be examined using postexpedition multimethod applications to comprehensively characterize and date event deposits. Detailed work will include detailed characterization of the sedimentologic, physical, and (bio-)geochemical features; stratigraphic expressions of relationships; and spatiotemporal distribution of event beds. These will be analyzed as foundational proxy evidence for distinguishing giant earthquakes from smaller earthquakes and aseismic processes driving mechanisms to ultimately develop a long-term record of giant earthquakes. Furthermore, Expedition 386 achievements comprise the first ever high temporal and high spatial resolution subsurface investigation and sampling in a hadal oceanic trench, which are the deepest and least explored environments on our planet. Preliminary initial results show high total organic carbon content and downcore pore water and headspace gas profiles with characteristic changes related to organic matter degradation. In combination, these are suggestive of the occurrence of intensive remineralization and reveal evidence of non-steady state behavior. Together with the successful offshore sampling for microbiology postexpedition analyses and research, this provides exciting new perspectives to advance our understanding of deep-sea elemental cycles and their influence on hadal environments. 

International Ocean Discovery Program (IODP) Expedition 386, Japan Trench Paleoseismology (offshore period: 13 April to 1 June 2021; Onshore Science Party: 14 February to 14 March 2022) was designed to test the concept of submarine paleoseismology in the Japan Trench, the area where the last, and globally only one out of four instrumentally-recorded, giant (i.e. magnitude 9 class) earthquake occurred back in 2011. “Submarine paleoseismology” is a promising approach to investigate deposits from the deep sea, where earthquakes leave traces preserved in the stratigraphic succession, to reconstruct the long-term history of earthquakes and to deliver observational data that help to reduce uncertainties in seismic hazard assessment for long return periods. This expedition marks the first time, giant piston coring (GPC) was used in IODP, and also the first time, partner IODP implementing organizations cooperated in jointly implementing a mission-specific platform expedition. We successfully collected 29 GPCs at 15 sites (1 to 3 holes each; total core recovery 831 meters), recovering 20 to 40-meter-long, continuous, upper Pleistocene to Holocene stratigraphic successions of 11 individual trench-fill basins along an axis-parallel transect from 36°N – 40.4°N, at water depth between 7445-8023 m below sea level. These offshore expedition achievements reveal the first high-temporal and high spatial resolution investigation and sampling of a hadal oceanic trench, that form the deepest and least explored environments on our planet. The cores are currently being examined by multimethod applications to characterize and date hadal trench sediments and extreme event deposits, for which the detailed sedimentological, physical and (bio-)geochemical features, stratigraphic expressions and spatiotemporal distribution will be analyzed for proxy evidence of giant earthquakes and (bio-)geochemical cycling in deep sea sediments. Initial preliminary results presented in this EGU presentation reveal event-stratigraphic successions comprising several 10s of potentially giant-earthquake related event beds, revealing a fascinating record that will unravel the earthquake history of the different along-strike segments that is 10–100 times longer than currently available information. Post-Expedition research projects further analyzing these initial IODP data sets will (i) enable statistically robust assessment of the recurrence patterns of giant earthquakes, there while advancing our understanding of earthquake induced geohazards along subduction zones and (ii) provide new constraints on sediment and carbon flux of event-triggered sediment mobilization to a deep-sea trench and its influence on the hadal environment. IODP Expedition 386 Science Party: Piero Bellanova; Morgane Brunet; Zhirong Cai; Antonio Cattaneo; Tae Soo Chang; Kanhsi Hsiung; Takashi Ishizawa; Takuya Itaki; Kana Jitsuno; Joel Johnson; Toshiya Kanamatsu; Myra Keep; Arata Kioka; Christian Maerz; Cecilia McHugh; Aaron Micallef; Luo Min; Dhananjai Pandey; Jean Noel Proust; Troy Rasbury; Natascha Riedinger; Rui Bao; Yasufumi Satoguchi; Derek Sawyer; Chloe Seibert; Maxwell Silver; Susanne Straub; Joonas Virtasalo; Yonghong Wang; Ting-Wei Wu; Sarah Zellers 

Short historical and even shorter instrumental records limit our perspective of earthquake maximum magnitude and recurrence, and thus are inadequate to fully characterize Earth’s complex and multiscale seismic behavior and its consequences. Examining prehistoric events preserved in the geological record is essential to reconstruct the long-term history of earthquakes and to deliver observational data that help to reduce uncertainties in seismic hazard assessment for long return periods. Motivated by the mission to fill the gap in long-term records of giant (Mw 9 class) earthquakes such as the Tohoku-Oki earthquake in 2011, International Ocean Discovery Program (IODP) Expedition 386, Japan Trench Paleoseismology, was designed to test and further develop submarine paleoseismology in the Japan Trench. Earthquake rupture propagation to the trench and sediment remobilization related to the 2011 Mw 9.0 Tohoku-Oki earthquake, and the respective structures and deposits are preserved in trench basins formed by flexural bending of the subducting Pacific Plate. These basins are ideal study areas for testing event deposits for earthquake triggering as they have poorly connected sediment transport pathways from the shelf and experience high sedimentation rates and low benthos activity (and thus high preservation potential) in the ultra-deep water hadal environment. Results from conventional coring covering the last ~1,500 y reveal good agreement between the sedimentary record and historical documents. Subbottom profile data are consistent with basin-fill successions of episodic muddy turbidite deposition and thus define clear targets for paleoseismologic investigations on longer timescales accessible only by deeper coring. In 2021, IODP Expedition 386 successfully collected 29 Giant Piston cores at 15 sites (1 to 3 holes each; total core recovery 831 meters), recovering 20 to 40-meter-long, continuous, upper Pleistocene to Holocene stratigraphic successions of 11 individual trench-fill basins along an axis parallel transect from 36°N – 40.4°N, at water depth between 7445-8023 m below sea level. The cores are currently being examined by multi-method applications to characterize and date event deposits for which the detailed stratigraphic expressions and spatiotemporal distribution will be analyzed for proxy evidence of giant versus smaller earthquakes versus other driving mechanisms. Initial preliminary results presented in this EGU presentation reveal event-stratigraphic successions comprising several 10s of potentially giant-earthquake related event beds, revealing a fascinating record that will unravel the earthquake history of the different along-strike segments, that is 10–100 times longer than currently available information. The data set will enable a statistically robust assessment of the recurrence patterns of giant earthquakes as input for improved probabilistic seismic hazard assessment and advanced understanding of earthquake induced geohazards globally. IODP Expedition 386 Science Party: Piero Bellanova; Morgane Brunet; Zhirong Cai; Antonio Cattaneo; Tae Soo Chang; Kanhsi Hsiung; Takashi Ishizawa; Takuya Itaki; Kana Jitsuno; Joel Johnson; Toshiya Kanamatsu; Myra Keep; Arata Kioka; Christian Maerz; Cecilia McHugh; Aaron Micallef; Luo Min; Dhananjai Pandey; Jean Noel Proust; Troy Rasbury; Natascha Riedinger; Rui Bao; Yasufumi Satoguchi; Derek Sawyer; Chloe Seibert; Maxwell Silver; Susanne Straub; Joonas Virtasalo; Yonghong Wang; Ting-Wei Wu; Sarah Zellers 

During Expedition 386, two Giant Piston Corer (GPC) system deployments in the northern study area (Basin S3) of the southern Japan Trench (Figure F1) resulted in the recovery of cores from four holes at Site M0091 (Figure F2). The water depth was between 7802 and 7812 meters below sea level (mbsl). A breakdown of operational time is reported weekly instead of daily (see OPS in Supplementary material) due to decisions to move between sites based on weather and current conditions. Holes at Site M0091 were cored during Week 6 of the offshore phase. In total, 51.94 m of cores (Table T1) and 53.5 km of hydroacoustic profiles (see Hydroacoustics) were recovered and acquired, respectively, in the focus area. Further operations details, including winch log and inclinometer information, are found for all sites in Coring methodology in the Expedition 386 methods chapter (Strasser et al., 2023a) and associated files (see PALEOMAG and WINCHLOGS in Supplementary material). 

During Expedition 386, one Giant Piston Corer (GPC) system deployment at Basin C/N1 in the boundary area between the central and northern Japan Trench (Figure F1) resulted in the recovery of cores from two holes at Site M0093 (Figure F2). The water depth was 7454 m below sea level (mbsl). A breakdown of operational time is reported weekly instead of daily (see OPS in Supplementary material) due to decisions to move between sites based on weather and current conditions. Holes at Site M0093 were cored during Week 7 of the offshore phase. In total, 26.91 m of cores (Table T1) and 3.89 km of hydroacoustic profiles (see Hydroacoustics) were recovered and acquired, respectively, in this focus area. Further operations details, including winch log and inclinometer information, are found for all sites in Coring methodology in the Expedition 386 methods chapter (Strasser et al., 2023a) and associated files (see PALEOMAG and WINCHLOGS in Supplementary material). 

During Expedition 386, one Giant Piston Corer (GPC) system deployment at the boundary area between the central and northern Japan Trench (Figure F1) resulted in the recovery of cores from two holes at Site M0094 (Figure F2). The water depth was 7469 meters below sea level (mbsl). A breakdown of operational time is reported weekly instead of daily (see OPS in Supplementary materials) due to decisions to move between sites based on weather and current conditions. Holes at Site M0094 were acquired during Week 7 of the offshore phase. In total, 19.065 m of cores (Table T1) and 5.8 km of hydroacoustic profiles (see Hydroacoustics) were recovered and acquired in this focus area. Further operations details, including winch log and inclinometer information, are found for all sites in Coring methodology in the Expedition 386 methods chapter (Strasser et al., 2023a) and associated files (see PALEOMAG and WINCHLOGS in Supplementary materials). 

During Expedition 386, a total of five Giant Piston Corer (GPC) system deployments in the central Japan Trench (Basin C2; Figure F1) resulted in the recovery of cores from six holes at Site M0083 and four at Site M0089 (Figure F2). The water depth ranged 7602–7626 meters below sea level (mbsl). A breakdown of operational time is reported weekly instead of daily (see OPS in Supplementary material) due to decisions to move between sites based on weather and current conditions. Sites M0083 and M0089 were cored during Weeks 2–4 of the offshore phase. In this focus area, a total of 154 m of cores (Table T1) were recovered. In addition, 121 km of hydroacoustic profiles (see Hydroacoustics) were acquired. Further operations details, including winch log and inclinometer information for all sites, are found in Coring methodology in the Expedition 386 methods chapter (Strasser, 2023a) and associated files (see PALEOMAG and WINCHLOGS in Supplementary material). 

During Expedition 386, a total of five Giant Piston Corer (GPC) system deployments in the northern Japan Trench (Basin N3; Figure F1) resulted in the recovery of cores from six holes at Site M0084 and four at Site M0085 (Figure F2). The water depth was between 7590 and 7603 meters below sea level (mbsl). A breakdown of operational time is reported weekly instead of daily (see OPS in Supplementary material) due to decisions to move between sites based on weather and current conditions. Cores from Sites M0084 and M0085 were acquired during Weeks 2, 3, and 5 of the offshore phase. In total, 149.2 m of cores (Table T1) and 133 km of hydroacoustic profiles (see Hydroacoustics) were recovered and acquired, respectively, in this focus area. Further operations details, including winch log and inclinometer information, are found for all sites in Coring methodology in the Expedition 386 methods chapter (Strasser et al., 2023a) and in the associated files (see PALEOMAG and WINCHLOGS in Supplementary material).