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1. Crustal-Scale Seismic Structure From Trench to Forearc in the Cascadia Subduction Zone: Crustal Model From Trench to Forearc

   https://doi.org/10.1002/2017JB014299  

   Rathnayaka, Sampath; Gao, Haiying (September 2017, Journal of Geophysical Research: Solid Earth)
2. Subduction Zone Obliquity Dictates Global Trench‐Parallel Inner Forearc Deformation

   https://doi.org/10.1029/2024AV001468  

   Morell, Kristin_D; Gilroy, Kellan; Finley, Theron; Harrichhausen, Nicolas (February 2025, AGU Advances)

   Abstract Although subduction zones are characterized by convergence, the upper plates of subduction zones exhibit a diverse range of deformation styles that are often inconsistent with regional convergence. While several theories have been proposed to explain these variations, the underlying factors driving these differences are still not fully understood. In this study, we analyze 24,000 km of active global subduction zones around the globe to determine how subduction zone obliquity affects deformation in the trench‐parallel and horizontal directions on land above subduction zones. We take advantage of recently published worldwide data sets of Global Navigation Satellite System (GNSS) velocities and global active fault catalogs in order to examine deformation at 13 of the world's forearcs. We analyze deformation over both short (decadal) timescales, captured by GNSS, and long (millennial to million‐year) timescales, observed through trench‐parallel active forearc faults. The results reveal a strong link between subduction obliquity and both the sense and amount of forearc rotation detected by GNSS, as well as the sense and rate of deformation along trench‐parallel strike‐slip faults. Unlike previous studies indicating that subduction obliquity affects forearc deformation only beyond a certain threshold, we demonstrate that even low to moderate obliquity significantly influences the observed deformation. 

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3. Sub-magmatic arc underplating by trench and forearc materials in shallow subduction systems; A geologic perspective and implications

   https://doi.org/10.1016/j.earscirev.2018.08.001  

   Ducea, Mihai N.; Chapman, Alan D. (October 2018, Earth-Science Reviews)
4. Japan Trench Paleoseismology

   https://doi.org/10.14379/iodp.proc.386.2023  

   Strasser, M; Ikehara, K; Everest, J (November 2023, Proceedings of the International Ocean Discovery Program Expedition reports)

   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. 

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5. Tracking past earthquakes along the Japan Trench: Fresh initial results from the IODP Japan Trench Paleoseismology Project

   https://doi.org/10.5194/egusphere-egu22-1588  

   Strasser, M; Ikehara, K; Everst, J.; Meada, L.; The Science Party of IODP Expedition 386 (June 2022, European Geophysical Union General Assembly)

   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 

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