Azores–Gibraltar transform fault

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The Azores–Gibraltar Transform Fault stretches from the Strait of Gibraltar and the Azores Triple Junction

The Azores–Gibraltar Transform Fault (AGFZ), also called a fault zone and a fracture zone, is a major seismic fault in the Central Atlantic Ocean west of the Strait of Gibraltar. It is the product of the complex interaction between the African, Eurasian, and Iberian plates. The AGFZ produced the large-magnitude 1755 Lisbon and 1969 Horseshoe earthquakes and, consequently, a number of large tsunamis.

Forming the Atlantic segment of the boundary between the African and Eurasian plates, the AGFZ is largely dominated by compressional forces between these converging (3.8–5.6 mm/yr) plates, but it is subject of a dynamic tectonic regime also involving extension, transcurrent, and compression. The oceanic lithosphere in the area is directly related to the opening of the North Atlantic Ocean and one of the oldest preserved on Earth.

The western end of the AGFZ, the Azores Triple Junction on the Mid-Atlantic Ridge (MAR), is where the North American, African, and Eurasian plates meet. Spreading in the MAR is faster south of the AGFZ than north of it, which results in a trancurrent movement along the AGFZ at about 4 mm/a (0.0050 in/Ms). The eastern segment of the fault is complex and characterised by a series of seamounts and ridges separating the Tores and Horseshoe abyssal plains. The active compressional deformation in this segment is an extremely rare example of compression between two oceanic litospheres.

The Atlantic Ocean is surrounded by passive margins with the exception of three subduction zones: the Lesser Antilles Arc, Scotia Arc, and the Gibraltar Arc. The Gibraltar Arc in the western Mediterranean is propagating westward into the Atlantic over an east-dipping oceanic slab. This subduction/back-arc basin system is developing along the AGFZ in front of the Alboran Block (under the Alboran Sea) at a rate faster than that of the Africa-Iberia convergence. Consequently, this area is a rare case of a passive margin slowly being transformed into an active margin. In the context of the Wilson Cycle, this indicate that the beginning of the closure of the Atlantic is taking place at the three Atlantic subduction zones.

References

Sources

• Duarte, J. C.; Rosas, F. M.; Terrinha, P.; Schellart, W. P.; Boutelier, D.; Gutscher, M. A.; Ribeiro, A. (2013). "Are subduction zones invading the Atlantic? Evidence from the southwest Iberia margin" (PDF). Geology. 41 (8): 839–842. doi:10.1130/G34100. {{cite journal}}: Invalid |ref=harv (help)
• Martínez‐Loriente, S.; Sallarès, V.; Gràcia, E.; Bartolome, R.; Dañobeitia, J. J.; Zitellini, N. (2014). "Seismic and gravity constraints on the nature of the basement in the Africa‐Eurasia plate boundary: New insights for the geodynamic evolution of the SW Iberian margin" (PDF). Journal of Geophysical Research: Solid Earth. 119 (1): 127–149. doi:10.1002/2013JB010476. Retrieved 29 October 2016. {{cite journal}}: Invalid |ref=harv (help)
• Richardson, S.; Musson, R.; Horsburgh, K. (2006). Tsunamis–Assessing the hazard for the UK and Irish coast (PDF (7.8Mb)). 41st Defra Flood and Coastal Management Conference. York, UK. Retrieved 29 October 2016. {{cite conference}}: Invalid |ref=harv (help)