Hellenic arc

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Hellenic arc
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A combined diagram of the Aegean and Anatolian Plates. The southern margin of the Hellenic arc is shown, which is the trend line of the faults separating the arc and the Hellenic Trench. The body of the arc is the chain called the outer Hellenides, which includes west Peloponnesus, Crete, Rhodes, southwestern Turkey, and all the islands between.
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middle arc
Hellas and the Aegean Sea
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middle arc
middle arc (Greece)
EtymologyRepublic of Hellas (Greece)
Geography
LocationThe center of Crete is at about center of the arc
Coordinates 35°12′50″N24°58′01″E / 35.21389°N 24.96694°E / 35.21389; 24.96694 Coordinates: 35°12′50″N24°58′01″E / 35.21389°N 24.96694°E / 35.21389; 24.96694
Archipelagosouthern outer Hellenides
Adjacent bodies of waterAegean Sea, Ionian Sea, Mediterranean Sea
Administration
Greece

The Hellenic arc or Aegean arc is an arcuate mountain chain of the southern Aegean Sea located on the southern margin of the Aegean Sea Plate. Geologically it results from the subduction of the African Plate under it along the Hellenic subduction zone. The Hellenic Trench trends parallel to its southern side. The Aegean Sea Plate, a microplate, is often considered part of the Eurasian Plate from which it is in the process of diverging. The arc itself is mainly marine, the mountaintops appearing as islands in the Ionian Sea, Crete and its environs, or in the Dodecanese group. It encroaches on mainland terrain in the Peloponnesus, on Crete, on Rhodes, and on the southern coast of Anatolia, thus being encompassed by both Greece and Turkey.

Contents

The direction of subduction is northward. Locations on the arc or near it on the north side are therefore called "outer" as they are at the outer margin of the plate. Locations further north are "inner." Generally the motion of subduction is from outer to inner. It so happens that, due to back-arc extension, the Hellenic Arc and Trench are moving in the reverse direction, from inner to outer, accounting for the severe arcuate form. There are in essence two layers at the subduction zone, a bottom one moving from outer to inner, and a top one moving from inner to outer.

The extension of the top layer required for this excursion of the arc and the trench comes from thinning of the back-arc ("in back of the arc"), weakening the crust there. There was already a mountain chain north of the arc, a legacy from the Alpine Orogeny, called the "inner arc." Its tops are the Cyclades. In addition, a chain of volcanos has appeared across it, due to magma breaking through the weakened crust; hence, this "inner arc" is termed the South Aegean Volcanic Arc. The two arcs are considered distinct, being from different orogenies. The term "Hellenic Arc" most often refers to the marginal, or "non-volcanic" arc, also called the Aegean forearc in the direction from outer to inner, which is consonant with the Hellenic Trench being the foredeep.

Geometry of the Hellenic arc

The Hellenic arc extends from the Ionian islands in the west to just east of the island of Rhodes in the east, where it links to the Cyprus arc.

Development

The current geometry of the Hellenic arc is a result of the southwards migration of the subduction zone. [1] This has led to extension both along the line of the arc as it bulged out and extension perpendicular to the arc, which is the current tectonic state.

Seismicity

The Hellenic arc is one of the most active seismic zones in western Eurasia. [2] It has regularly been the source for magnitude 7 earthquakes in the last hundred years of instrumental recording and the location for at least two historical events that were probably of about magnitude 8 or more, the 365 Crete earthquake and the 1303 Crete earthquake. [3]

See also


Related Research Articles

Oceanic trench Long and narrow depressions of the sea floor

Oceanic trenches are prominent long, narrow topographic depressions of the ocean floor. They are typically 50 to 100 kilometers wide and 3 to 4 km below the level of the surrounding oceanic floor, but can be thousands of kilometers in length. There are about 50,000 kilometers (31,000 mi) of oceanic trenches worldwide, mostly around the Pacific Ocean, but also in the eastern Indian Ocean and a few other locations. The greatest ocean depth measured is in the Challenger Deep of the Mariana Trench, at a depth of 11,034 m (36,201 ft) below sea level.

Subduction A geological process at convergent tectonic plate boundaries where one plate moves under the other

Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the heavier plate dives beneath the second plate and sinks into the mantle. A region where this process occurs is known as a subduction zone, and its surface expression is known as an arc-trench complex. The process of subduction has created most of the Earth's continental crust. Rates of subduction are typically measured in centimeters per year, with the average rate of convergence being approximately two to eight centimeters per year along most plate boundaries.

Convergent boundary Region of active deformation between colliding tectonic plates

A convergent boundary is an area on Earth where two or more lithospheric plates collide. One plate eventually slides beneath the other, a process known as subduction. The subduction zone can be defined by a plane where many earthquakes occur, called the Wadati–Benioff zone. These collisions happen on scales of millions to tens of millions of years and can lead to volcanism, earthquakes, orogenesis, destruction of lithosphere, and deformation. Convergent boundaries occur between oceanic-oceanic lithosphere, oceanic-continental lithosphere, and continental-continental lithosphere. The geologic features related to convergent boundaries vary depending on crust types.

Island arc Arc-shaped archipelago formed by intense seismic activity of long chains of active volcanoes

Island arcs are long chains of active volcanoes with intense seismic activity found along convergent tectonic plate boundaries. Most island arcs originate on oceanic crust and have resulted from the descent of the lithosphere into the mantle along the subduction zone. They are the principal way by which continental growth is achieved.

Forearc The region between an oceanic trench and the associated volcanic arc

A forearc is the region between an oceanic trench and the associated volcanic arc. Forearc regions are found at convergent margins, and include any accretionary wedge and forearc basin that may be present. Due to tectonic stresses as one tectonic plate rides over another, forearc regions are sources for great thrust earthquakes.

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A volcanic arc is a chain of volcanoes formed above a subducting plate, positioned in an arc shape as seen from above. Offshore volcanoes form islands, resulting in a volcanic island arc. Generally, volcanic arcs result from the subduction of an oceanic tectonic plate under another tectonic plate, and often parallel an oceanic trench. The oceanic plate is saturated with water, and volatiles such as water drastically lower the melting point of the mantle. As the oceanic plate is subducted, it is subjected to greater and greater pressures with increasing depth. This pressure squeezes water out of the plate and introduces it to the mantle. Here the mantle melts and forms magma at depth under the overriding plate. The magma ascends to form an arc of volcanoes parallel to the subduction zone.

Ryukyu Trench Oceanic trench along the southeastern edge of Japans Ryukyu Islands in the Pacific Ocean

The Ryukyu Trench, also called Nansei-Shotō Trench, is a 1398 km (868 mi) long oceanic trench located along the southeastern edge of Japan's Ryukyu Islands in the Philippine Sea in the Pacific Ocean, between northeastern Taiwan and southern Japan. The trench has a maximum depth of 7460 m (24,476 ft). The trench is the result of oceanic crust of the Philippine Plate obliquely subducting beneath the continental crust of the Eurasian Plate at a rate of approximately 52 mm/yr. In conjunction with the adjacent Nankai Trough to the northeast, subduction of the Philippine plate has produced 34 volcanoes. The largest earthquake to have been recorded along the Ryukyu Trench, the 1968 Hyūga-nada earthquake, was magnitude 7.5 and occurred along the northernmost part of the trench on 1 April 1968. This earthquake also produced a tsunami.

Pleistos

The Pleistos is a river in central Greece. It drains the Pleistos valley, named after it, a relatively recent rift valley north of the Gulf of Corinth, and parallel to it. They have the same geologic causes. Being situated in karst topography, much of the river runs or seeps through underground channels. The surface stream is intermittent. However, the limestone riverbed reflecting the light gives the appearance of a stream of water.

Izu–Bonin–Mariana Arc

The Izu–Bonin–Mariana (IBM) arc system is a tectonic plate convergent boundary in Micronesia. The IBM arc system extends over 2800 km south from Tokyo, Japan, to beyond Guam, and includes the Izu Islands, the Bonin Islands, and the Mariana Islands; much more of the IBM arc system is submerged below sealevel. The IBM arc system lies along the eastern margin of the Philippine Sea Plate in the Western Pacific Ocean. It is the site of the deepest gash in Earth's solid surface, the Challenger Deep in the Mariana Trench.

Accretionary wedge The sediments accreted onto the non-subducting tectonic plate at a convergent plate boundary

An accretionary wedge or accretionary prism forms from sediments accreted onto the non-subducting tectonic plate at a convergent plate boundary. Most of the material in the accretionary wedge consists of marine sediments scraped off from the downgoing slab of oceanic crust, but in some cases the wedge includes the erosional products of volcanic island arcs formed on the overriding plate.

South Aegean Volcanic Arc Chain of volcanic islands in the South Aegean Sea

The South Aegean Volcanic Arc is a volcanic arc in the South Aegean Sea formed by plate tectonics. The prior cause was the subduction of the African plate beneath the Eurasian plate, raising the Aegean arc across what is now the north Aegean Sea. It was not yet the sea, nor an arc, or at least not the one it is today, nor was there a chain of volcanoes. In the Holocene the process of back-arc extension began, probably stimulated by pressure from the Arabian Plate compressing the region behind the arc. The extension deformed the region into its current configuration. First, the arc moved to the south and assumed its arcuate configuration. Second, the Aegean Sea opened behind the arc because the crust was thinned and weakened there. Third, magma broke through the thinned crust to form a second arc composed of a volcanic chain. And finally, the Aegean Sea Plate broke away from Eurasia in the new fault zone to the north.

Aegean Sea Plate A small tectonic plate in the eastern Mediterranean Sea

The Aegean Sea Plate is a small tectonic plate located in the eastern Mediterranean Sea under southern Greece and far western Turkey. Its southern edge is a subduction zone south of Crete, where the African Plate is being swept under the Aegean Sea Plate. To the north is the Eurasian Plate, which is a divergent boundary responsible for the formation of the Gulf of Corinth.

This is a list of articles related to plate tectonics and tectonic plates.

Hellenic Trench Long narrow depression bordering the Aegean Sea to the south

The Hellenic Trench (HT) is an oceanic trough located in the forearc of the Hellenic Arc, an arcuate archipelago on the southern margin of the Aegean Sea Plate, or Aegean Plate, also called Aegea, the basement of the Aegean Sea. The HT begins in the Ionian Sea near the mouth of the Gulf of Corinth and curves to the south, following the margin of the Aegean Sea. It passes close to the south shore of Crete and ends near the island of Rhodes just offshore Anatolia.

The 1303 Crete earthquake occurred at about dawn on 8 August at 6:00 local time. It had an estimated magnitude of about 8, a maximum intensity of IX (Violent) on the Mercalli intensity scale, and triggered a major tsunami that caused severe damage and loss of life on Crete and at Alexandria. It badly damaged the Lighthouse of Alexandria.

The 1810 Crete earthquake occurred at 22:15 on 16 February. It caused great destruction in Heraklion, some damage from Malta to northern Egypt and was felt from central Italy to Syria. 2,000 fatalities were reported from Candia (Heraklion).

The Sumatra Trench is a part of the Sunda Trench or Java Trench. The Sunda subduction zone is located in the east part of Indian Ocean, and is about 300 km (190 mi) from the southwest coast of Sumatra and Java islands. It extends over 5,000 km (3,100 mi) long, starting from Myanmar in the northwest and ending at Sumba Island in the southeast.

The 1956 Amorgos earthquake occurred at 03:11 UTC on July 9. It had a magnitude of 7.7 on the moment magnitude scale and a maximum perceived intensity of IX on the Mercalli intensity scale. The epicentre was to the south of the island of Amorgos, the easternmost island of the Cyclades in the Aegean Sea. There was significant damage on Amorgos and the neighbouring island of Santorini. It was the largest earthquake in Greece in the 20th century. It was followed 13 minutes later by a magnitude 7.2 earthquake near Santorini. It triggered a major tsunami with a maximum run-up of 30 m. The combined effects of the earthquake shaking and the tsunami caused the deaths of 53 people with a further 100 injured.

Hellenic subduction zone

The Hellenic subduction zone (HSZ) is the convergent boundary between the African Plate and the Aegean Sea Plate, where oceanic crust of the African is being subducted north–northeastwards beneath the Aegean. The southernmost and shallowest part of the zone is obscured beneath the deformed thick sedimentary sequence that forms the Mediterranean Ridge accretionary complex. It has a well-defined Wadati–Benioff zone of seismicity, which demonstrates the relatively shallow dip of its southern part, which increases markedly to the north of the non-volcanic part of the Hellenic arc. The descending slab has been imaged using seismic tomography down to the top of the mantle transition zone at 410 km depth.

Oblique subduction

Oblique subduction is a form of subduction for which the convergence direction differs from 90° to the plate boundary. Most convergent boundaries involve oblique subduction, particularly in the Ring of Fire including the Ryukyu, Aleutian, Central America and Chile subduction zones. In general, the obliquity angle is between 15° to 30°. Subduction zones with high obliquity angles include Sunda trench and Ryukyu arc.

References

  1. ten Veen, J.H.; Kleinspehn, K.L. (2003). "Incipient continental collision and plate-boundary curvature: Late Pliocene–Holocene transtensional Hellenic forearc, Crete, Greece". Journal of the Geological Society. 160 (2): 161–181. Bibcode:2003JGSoc.160..161T. doi:10.1144/0016-764902-067 . Retrieved 26 July 2010.
  2. Papadopoulos, G. A.; Ganas, A.; Karastathis, C. (2004). "Seismicity Properties as a Marker of the Active Plate Convergence in the western Hellenic Arc". American Geophysical Union, Fall Meeting Abstracts. 53: 0483. Bibcode:2004AGUFM.T53B0483P.
  3. USGS (29 March 2010). "Tectonic Summary of Greece" . Retrieved 26 July 2010.

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