Large intraplate earthquakes on an extinct oceanic plate reveal fracture zone reactivation

Oceanic fracture zones, the inactive traces of former transform faults, are often considered tectonically inactive once relative plate motion across them ceases. However, their long-term mechanical behavior and role in intraplate deformation remain poorly understood. Here, we analyze two earthquakes of Mw 7.5 and Mw 7.6 that occurred about 15 km and 49 days apart in 2025 within the Phoenix Plate, along a structure spatially consistent with a former oceanic transform fault in the Drake Passage region. These events indicate that such structures remain lithosphere-scale zones of mechanical weakness and can be reactivated under present-day stress conditions. We propose here that inherited fault geometry and regional far-field stresses associated with Scotia–Antarctic plate interactions collectively promote strain localization on these presumed fossil structures. Our results indicate that the cessation of plate-boundary activity does not imply mechanical quiescence, and that oceanic fracture zones represent long-lived zones of intraplate weakness that can both host large-magnitude earthquakes and facilitatevolcanic emplacement, as shown by a seismic reflection profile crossing the fracture zone near the earthquake epicenters. This structure acts as a lithosphere-scale tear fault within the slow subducting Phoenix slab beneath the South Shetland continental block. This behavior has implications for the mechanical evolution of oceanic lithosphere and for the interpretation of intraplate seismicity near extinct plate boundaries. Cessation of plate-boundary activity at oceanic fracture zones does not imply mechanical quiescence, these can be reactivated under present-day stress conditions, shown through analysis of two earthquakes that occurred in 2025 within the former Phoenix Plate in the Drake Passage region.