The Azores–Gibraltar Fault Zone is the submarine plate boundary between the African and Eurasian plates, stretching across the Atlantic from the Azores triple junction eastward toward the Strait of Gibraltar. It changes character along its length, from spreading and transform motion near the Azores to slow convergence off Portugal and Morocco.
In its eastern part, southwest of Cape St. Vincent, the boundary becomes diffuse and compressional, with poorly mapped thrust faults where Africa presses against Iberia. This offshore convergence is capable of generating very large but infrequent earthquakes and, because it lies under deep water, dangerous tsunamis.
This zone is the suspected source of the catastrophic 1755 Lisbon earthquake (estimated magnitude 8.5 to 9), which destroyed the Portuguese capital and sent a tsunami across the Atlantic that struck Portugal, Spain and Morocco. The 1969 Gorringe Bank earthquake (magnitude 7.8) confirmed the region's continued capacity for major offshore ruptures.