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To explore controls on megathrust behavior and its connection with forearc deformation, we studied the Andreanof segment of the Aleutian Subduction Zone (offshore Alaska, USA), which has a simple geological history as a relatively young intra-oceanic subduction zone. Here, the forearc shows greater uplift and compression in the strongly coupled Adak region compared to the weakly coupled Atka region. Using multichannel seismic reflection data, we found that the incoming plate in both regions exhibits similar characteristics along the segment, suggesting that its properties do not account for the varying megathrust behavior and forearc deformation. Instead, differences between the Atka and Adak regions in the thickness of the methane hydrate stability zone, as marked by a bottom-simulating reflector, suggest more heat advection, and thus dewatering, in the Adak region, where the more developed fault network may enable fluid drainage, thereby lowering pore pressure at the megathrust and promoting coupling. Higher coupling allows for seismic and stress cycling that would sustain forearc permeability by faulting. Our results suggest a feedback between deformation and coupling that may be active or latent in other more complex subduction zones but in concert with or masked by other factors. 

Abstract Geological processes at subduction zones and their associated geohazards (e.g., megathrust earthquakes, submarine landslides, tsunamis, and arc volcanism) are, to a large extent, controlled by the structure, physical properties and fluid content of the subducting plate, the accreted sediments, and the overriding plate. In these settings, modern seismic modeling and imaging techniques based on controlled-source, multicomponent ocean-bottom seismometer (OBS) data are some of the best tools available for determining the subseafloor elastic properties, which can be linked to the aforementioned properties. Here, we present CASIE21-OBS, a controlled-source marine wide-angle OBS data set recently collected across the Cascadia convergent margin as part of the larger CAscadia Seismic Imaging Experiment 2021 (CASIE21). The main component of CASIE21 is a long-offset multichannel seismic (MCS) survey of the Cascadia margin conducted in June–July 2021 onboard R/V M.G. Langseth (cruise MGL2104) aiming to characterize the incoming plate, the plate interface geometry and properties, and the overlying sediment stratigraphy and physical properties. CASIE21-OBS was conducted during R/V M.G. Langseth cruise MGL2103 (May 2021) and R/V Oceanus cruise OC2106A (June–July 2021). It consisted of 63 short-period four-component OBSs deployed at a total 120 stations along 10 across-trench profiles extending from ∼50 km seaward of the deformation front to the continental shelf, and from offshore northern Vancouver Island to offshore southern Oregon. The OBSs recorded the airgun signals of the CASIE21-MCS survey as well as natural seismicity occurring during the deployment period (24 May 2021 19:00 UTC–9 July 2021 09:00 UTC). The OBS data are archived and available at the Incorporated Research Institutions for Seismology Data Management Center under network code YR_2021 for continuous time series (miniSEED) and identifier 21-008 for assembled data set (SEG-Y).