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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. 

Abstract Subduction forearcs are subject to seismic hazard from upper plate faults that are often invisible to instrumental monitoring networks. Identifying active faults in forearcs therefore requires integration of geomorphic, geologic, and paleoseismic data. We demonstrate the utility of a combined approach in a densely populated region of Vancouver Island, Canada, by combining remote sensing, historical imagery, field investigations, and shallow geophysical surveys to identify a previously unrecognized active fault, theXEOLXELEK‐Elk Lake fault, in the northern Cascadia forearc, ∼10 km north of the city of Victoria. Lidar‐derived digital terrain models and historical air photos show a ∼2.5‐m‐high scarp along the surface of a Quaternary drumlinoid ridge. Paleoseismic trenching and electrical resistivity tomography surveys across the scarp reveal a single reverse‐slip earthquake produced a fault‐propagation fold above a blind southwest‐dipping fault. Five geologically plausible chronological models of radiocarbon dated charcoal constrain the likely earthquake age to between 4.7 and 2.3 ka. Fault‐propagation fold modeling indicates ∼3.2 m of reverse slip on a blind, 50° southwest‐dipping fault can reproduce the observed deformation. Fault scaling relations suggest aM6.1–7.6 earthquake with a 13 to 73‐km‐long surface rupture and 2.3–3.2 m of dip slip may be responsible for the deformation observed in the paleoseismic trench. An earthquake near this magnitude in Greater Victoria could result in major damage, and our results highlight the importance of augmenting instrumental monitoring networks with remote sensing and field studies to identify and characterize active faults in similarily challenging environments.