Azores–Gibraltar Transform Fault

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.[1] The AGFZ produced the large-magnitude 1755 Lisbon and 1969 Horseshoe earthquakes and, consequently, a number of large tsunamis.[2]

Azores–Gibraltar Transform Fault is located in North Atlantic
Azores–Gibraltar Transform Fault
Azores–Gibraltar Transform Fault
The Azores–Gibraltar Transform Fault stretches between the Strait of Gibraltar and the Azores Triple Junction

Geologic setting

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 to 5.6 mm/a (0.15 to 0.22 in/year)) plates, but it is subject of a dynamic tectonic regime also involving extension and transform faulting. 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.[2]

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 (0.16 in/year).[1] 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.[1]

Plate tectonics

The Atlantic Ocean is surrounded by passive margins with the exception of three subduction zones: the Lesser Antilles Arc in the Caribbean, the Scotia Arc in the South Atlantic, and the Gibraltar Arc in the western Mediterranean. The Gibraltar Arc is propagating westward into the Atlantic over an east-dipping oceanic slab (one of the remainders of the Tethys Ocean). This subduction/back-arc basin system is developing 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.[3] The extension of this subduction system, known as the "allochthonous unit of the Gulf of Cadiz" (AUGZ), marks the continuing propagation of the Alpide belt into the Atlantic along the AGFZ.[4] In the context of the Wilson Cycle, this suggests that the beginning of the closure of the Atlantic is taking place in front of the three Atlantic subduction zones.[3]

References

Notes

  1. ^ a b c Richardson, Musson & Horsburgh 2006, Appendix A, Tectonics of the Azores-Gibraltar fault zone, pp. 94–97
  2. ^ a b Martínez‐Loriente et al. 2014, Introduction, p. 127
  3. ^ a b Duarte et al. 2013, Introduction, pp. 839–840
  4. ^ Hernández-Molina et al. 2016, Geologic framework, p. 4

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". Geology. 41 (8): 839–842. doi:10.1130/G34100 (inactive 2019-02-20).
  • Hernández-Molina, F. J.; Sierro, F. J.; Llave, E.; Roque, C.; Stow, D. A. V.; Williams, T.; Lofi, J.; Van der Schee, M.; Arnáiz, A.; Ledesma, S.; Rosales, C.; Rodríguez-Tovar, F. J.; Pardo-Igúzquiza, E.; Brackenridge, R. E. (2016). "Evolution of the gulf of Cadiz margin and southwest Portugal contourite depositional system: Tectonic, sedimentary and paleoceanographic implications from IODP expedition 339". Marine Geology. 377: 7–39. Bibcode:2016MGeol.377....7H. doi:10.1016/j.margeo.2015.09.013. Retrieved 29 October 2015.
  • 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". Journal of Geophysical Research: Solid Earth. 119 (1): 127–149. Bibcode:2014JGRB..119..127M. doi:10.1002/2013JB010476. Retrieved 29 October 2016.
  • Richardson, S.; Musson, R.; Horsburgh, K. (2006). Tsunamis–Assessing the hazard for the UK and Irish coast (PDF). 41st Defra Flood and Coastal Management Conference. York, UK. Archived from the original (PDF (7.8Mb)) on 23 January 2013. Retrieved 29 October 2016.

Coordinates: 37°N 16°W / 37°N 16°W

1755 Lisbon earthquake

The 1755 Lisbon earthquake, also known as the Great Lisbon earthquake, occurred in the Kingdom of Portugal on the morning of Saturday, 1 November, Feast of All Saints, at around 09:40 local time. In combination with subsequent fires and a tsunami, the earthquake almost totally destroyed Lisbon and adjoining areas. Seismologists today estimate the Lisbon earthquake had a magnitude in the range 8.5–9.0 on the moment magnitude scale, with its epicentre in the Atlantic Ocean about 200 km (120 mi) west-southwest of Cape St. Vincent. Chronologicaly it was the third known large scale earthquake to hit the city (one in 1321 and another in 1531). Estimates place the death toll in Lisbon alone between 10,000 and 100,000 people, making it one of the deadliest earthquakes in history.

The earthquake accentuated political tensions in the Kingdom of Portugal and profoundly disrupted the country's colonial ambitions. The event was widely discussed and dwelt upon by European Enlightenment philosophers, and inspired major developments in theodicy. As the first earthquake studied scientifically for its effects over a large area, it led to the birth of modern seismology and earthquake engineering.

1941 Gloria Fault earthquake

The 1941 Gloria Fault earthquake occurred at 18:03:57 UTC in the northern Atlantic Ocean on 25 November 1941. It had a magnitude of about 8.0 on the moment magnitude scale and a maximum perceived intensity of IX (Violent) on the Mercalli intensity scale. It was caused by movement on the Gloria Fault, part of the Azores–Gibraltar Transform Fault. It triggered a small tsunami, which was observed at Newlyn, Cornwall.

Atlantic Ocean

The Atlantic Ocean is the second largest of the world's oceans, with an area of about 106,460,000 square kilometers (41,100,000 square miles). It covers approximately 20 percent of the Earth's surface and about 29 percent of its water surface area. It separates the "Old World" from the "New World".

The Atlantic Ocean occupies an elongated, S-shaped basin extending longitudinally between Europe and Africa to the east, and the Americas to the west. As one component of the interconnected global ocean, it is connected in the north to the Arctic Ocean, to the Pacific Ocean in the southwest, the Indian Ocean in the southeast, and the Southern Ocean in the south (other definitions describe the Atlantic as extending southward to Antarctica). The Equatorial Counter Current subdivides it into the North Atlantic Ocean and the South Atlantic Ocean at about 8°N.Scientific explorations of the Atlantic include the Challenger expedition, the German Meteor expedition, Columbia University's Lamont-Doherty Earth Observatory and the United States Navy Hydrographic Office.

Azores

The Azores ( ə-ZORZ or AY-zorz; Portuguese: Açores, [ɐˈsoɾɨʃ]), officially the Autonomous Region of the Azores (Região Autónoma dos Açores), is one of the two autonomous regions of Portugal (along with Madeira (Região Autónoma da Madeira)). It is an archipelago composed of nine volcanic islands in the North Atlantic Ocean about 1,360 km (850 mi) west of continental Portugal, about 1,643 km (1,021 mi) west of Lisbon, in continental Portugal, about 1,507 km (936 mi) northwest of Morocco, and about 1,925 km (1,196 mi) southeast of Newfoundland, Canada.

Its main industries are agriculture, dairy farming, livestock, fishing, and tourism, which is becoming the major service activity in the region. In addition, the government of the Azores employs a large percentage of the population directly or indirectly in the service and tertiary sectors. The main capital of the Azores is Ponta Delgada.

There are nine major Azorean islands and an islet cluster, in three main groups. These are Flores and Corvo, to the west; Graciosa, Terceira, São Jorge, Pico, and Faial in the centre; and São Miguel, Santa Maria, and the Formigas Reef to the east. They extend for more than 600 km (370 mi) and lie in a northwest-southeast direction.

All the islands have volcanic origins, although some, such as Santa Maria, have had no recorded activity since the islands were settled. Mount Pico, on the island of Pico, is the highest point in Portugal, at 2,351 m (7,713 ft). If measured from their base at the bottom of the ocean to their peaks, which thrust high above the surface of the Atlantic, the Azores are actually some of the tallest mountains on the planet.

The climate of the Azores is very mild for such a northerly location, being influenced by its distance from the continents and by the passing Gulf Stream. Due to the marine influence, temperatures remain mild year-round. Daytime temperatures normally fluctuate between 16 °C (61 °F) and 25 °C (77 °F) depending on season. Temperatures above 30 °C (86 °F) or below 3 °C (37 °F) are unknown in the major population centres. It is also generally wet and cloudy.

The culture, dialect, cuisine, and traditions of the Azorean islands vary considerably, because these once-uninhabited and remote islands were settled sporadically over a span of two centuries.

Barbary macaques in Gibraltar

Originally from the Atlas mountains and the Rif mountains of Morocco, the Barbary macaque population in Gibraltar is the only wild monkey population on the European continent. Although most populations in Africa are experiencing declining populations due to hunting and deforestation, the population of Barbary monkeys in Gibraltar is increasing. Currently, some 300 animals in five troops occupy the Upper Rock area of the Gibraltar Nature Reserve, though they make occasional forays into the town. As they are a tailless species, they are also known locally as Barbary apes or rock apes, despite being monkeys (Macaca sylvanus). The local people simply refer to them as monos (English: monkeys) when conversing in Spanish or Llanito (the local vernacular).

Gibraltar pound

The Gibraltar pound (currency sign: £; banking code: GIP) is the currency of Gibraltar. It is pegged to – and exchangeable with – the British pound sterling at par value. Gibraltar pound coins are minted notes printed by the Government of Gibraltar.

Gibraltar real

The real was the official currency of Gibraltar until 1825 and continued to circulate alongside other Spanish and British currencies until 1898.

Ibrahim-al-Ibrahim Mosque

The Ibrahim-al-Ibrahim Mosque, also known as the King Fahd bin Abdulaziz al-Saud Mosque or the Mosque of the Custodian of the Two Holy Mosques, is a mosque located at Europa Point in the British overseas territory of Gibraltar, a peninsula connected to southern Spain. The mosque faces south towards the Strait of Gibraltar and Morocco several kilometres away.

List of earthquakes in 1941

This is a list of earthquakes in 1941. Only magnitude 6.0 or greater earthquakes appear on the list. Lower magnitude events are included if they have caused death, injury or damage. Events which occurred in remote areas will be excluded from the list as they wouldn't have generated significant media interest. All dates are listed according to UTC time. With 1,200 lives lost, Saudi Arabia experienced the heaviest death toll on January 11. Other deadly quakes occurred in Iran, Turkey, Taiwan, Burma, and China. There were 15 magnitude 7.0+ events altogether. The largest event was in the north Atlantic Ocean at the Azores–Gibraltar Transform Fault in November with a magnitude 8.0. Other large events struck India, Japan, and Mexico to name a few. Australia saw a couple of unusually large quakes this year.

List of earthquakes in 1969

This is a list of earthquakes in 1969. Only magnitude 6.0 or greater earthquakes appear on the list. Lower magnitude events are included if they have caused death, injury or damage. Events which occurred in remote areas will be excluded from the list as they wouldn't have generated significant media interest. All dates are listed according to UTC time. Maximum intensities are indicated on the Mercalli intensity scale and are sourced from United States Geological Survey (USGS) ShakeMap data. Activity generally was slightly below average with 14 events reaching magnitude 7 or greater. The largest event was off the coast of Portugal in February and measured 7.8. Other parts experiencing large events were Indonesia and Russia. The Americas had no events above magnitude 7 which is an uncommon occurrence. Of the 4,000 deaths from earthquakes two events dominated. Southeastern China had an earthquake of magnitude 5.7 in July which contributed 3,000 of the total. Indonesia had the bulk of the rest of the death toll.

List of fault zones

This list covers all faults and fault-systems that are either geologically important or connected to prominent seismic activity. It is not intended to list every notable fault, but only major fault zones.

Megathrust earthquake

Megathrust earthquakes occur at subduction zones at destructive convergent plate boundaries, where one tectonic plate is forced underneath another. These interplate earthquakes are the planet's most powerful, with moment magnitudes (Mw) that can exceed 9.0. Since 1900, all earthquakes of magnitude 9.0 or greater have been megathrust earthquakes. No other type of known terrestrial source of tectonic activity has produced earthquakes of this scale.

Outline of Gibraltar

The following outline is provided as an overview of and topical guide to Gibraltar:

Gibraltar – British Overseas Territory located near the southernmost tip of the Iberian Peninsula of Southeastern Europe overlooking the Strait of Gibraltar between the Mediterranean Sea and the North Atlantic Ocean. The territory shares a border with Spain to the north. Gibraltar was ceded by Spain to Great Britain in perpetuity in 1713 under the Treaty of Utrecht though Spain requests its return. The Government of the United Kingdom has stated it is committed to respecting the wishes of the Gibraltarians, who strongly oppose the idea of annexation along with any proposal for shared sovereignty with Spain.

Royal Patriarchal Music Seminary of Lisbon

The Royal Patriarchal Music Seminary of Lisbon (Portuguese: Real Seminário de Música da Patriarcal de Lisboa) was founded in 1713 by Portugal's king João V (John) (referred to, but not always in a complimentary manner, with soubriquets such as "The Magnanimous" (Portuguese:o Magnánimo) "The Magnificent" (Portuguese: o Magnifico), "The Portuguese Sun King" (Portuguese: o Rei-Sol Português) and even o Freirático (literally a "devotee of nuns")) to train singers for his Royal Chapel of Saint Thomas (Portuguese: capela de São Tomé) at Ribeira Palace (Portuguese: Paço da Ribeira) (See Illus. 1).

Its role was similar to that of other schools which for some centuries had been training singers and musicians for European abbeys, cathedrals, parish and collegiate churches, and court chapels. Over time, its influence expanded as it produced singers, instrumentalists and composers of merit, many of whom took on careers in sacred and secular music including opera outside Portugal.

According to the records (See Illus. 2), the official date of the Seminary's foundation was 9 April 1713, three years before the Patriarchate of Lisbon (Portuguese: Patriarcado de Lisboa) came into operation. At that early stage, the Seminary was housed in the Archbishop's Palace near Lisbon Cathedral, but from the outset, the Seminary's function and purpose were directly associated with the court, and once the position of Patriarch of Lisbon was created and the holder became chaplain to the king, the Seminary as part of the patriarchal household continued to serve its primary purpose in providing music in the Royal Chapel.

Although it was neither Portugal's first nor only music school associated with the church, the Seminary's location in Lisbon and its relationship with the monarchy placed it at the forefront of Portugal's music life at this time.

It remained the country's most important music school until it was closed in 1834 and replaced the following year by the Lisbon Conservatory (Portuguese: Conservatório de Música).According to one analysis, "In it [the Seminary] was formed the great majority of our most outstanding eighteenth-century composers" including Francisco António de Almeida, João Rodrigues Esteves, António Teixeira, José Joaquim dos Santos, António Leal Moreira and Marcos Portugal, among others.

Santa Maria Island

Santa Maria (Portuguese pronunciation: [ˈsɐ̃.tɐ mɐˈɾi.ɐ]), Portuguese for Saint Mary, is an island located in the eastern group of the Azores archipelago (south of the island of São Miguel) and the southernmost island in the Azores. The island is primarily known for its white sand beaches, distinctive chimneys, and dry warm weather.

Shrine of Our Lady of Europe

The Shrine of Our Lady of Europe is a Roman Catholic parish church and national shrine of Gibraltar located at Europa Point. The church is dedicated to Our Lady of Europe, the Catholic patroness of Gibraltar.

It belongs to the European Marian Network, which links twenty Marian sanctuaries in Europe (as many as the number of decades in the Rosary).

Strait of Gibraltar crossing

The Strait of Gibraltar crossing is a hypothetical bridge or tunnel spanning the Strait of Gibraltar (about 14 km or 9 miles at its narrowest point) that would connect Europe and Africa. The governments of Spain and Morocco appointed a joint committee to investigate the feasibility of linking the two continents in 1979, which resulted in the much broader Euromed Transport project.

Terceira Rift

The Terceira Rift is a geological rift located amidst the Azores islands in the Atlantic Ocean. It runs between the Azores Triple Junction to the west and the Azores–Gibraltar Transform Fault to the southeast. It separates the Eurasian Plate to the north from the African Plate to the south. The Terceira Rift is named for Terceira Island through which it passes.

Tsunami

A tsunami (from Japanese: 津波, "harbour wave";

English pronunciation: soo-NAH-mee or ) or tidal wave,, also known as a seismic sea wave, is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and other underwater explosions (including detonations, landslides, glacier calvings, meteorite impacts and other disturbances above or below water all have the potential to generate a tsunami. Unlike normal ocean waves, which are generated by wind, or tides, which are generated by the gravitational pull of the Moon and the Sun, a tsunami is generated by the displacement of water.

Tsunami waves do not resemble normal undersea currents or sea waves because their wavelength is far longer. Rather than appearing as a breaking wave, a tsunami may instead initially resemble a rapidly rising tide. For this reason, it is often referred to as a "tidal wave", although this usage is not favoured by the scientific community because it might give the false impression of a causal relationship between tides and tsunamis. Tsunamis generally consist of a series of waves, with periods ranging from minutes to hours, arriving in a so-called "internal wave train". Wave heights of tens of metres can be generated by large events. Although the impact of tsunamis is limited to coastal areas, their destructive power can be enormous, and they can affect entire ocean basins. The 2004 Indian Ocean tsunami was among the deadliest natural disasters in human history, with at least 230,000 people killed or missing in 14 countries bordering the Indian Ocean.

The Ancient Greek historian Thucydides suggested in his 5th century BC History of the Peloponnesian War that tsunamis were related to submarine earthquakes, but the understanding of tsunamis remained slim until the 20th century and much remains unknown. Major areas of current research include determining why some large earthquakes do not generate tsunamis while other smaller ones do; accurately forecasting the passage of tsunamis across the oceans; and forecasting how tsunami waves interact with shorelines.

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