The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At 103 million km2 (40 million sq mi), it is the largest tectonic plate.
A volcanic arc is a belt of volcanoes formed above a subducting oceanic tectonic plate, with the belt arranged in an arc shape as seen from above. Volcanic arcs typically parallel an oceanic trench, with the arc located further from the subducting plate than the trench. The oceanic plate is saturated with water, mostly in the form of hydrous minerals such as micas, amphiboles, and serpentines. As the oceanic plate is subducted, it is subjected to increasing pressure and temperature with increasing depth. The heat and pressure break down the hydrous minerals in the plate, releasing water into the overlying mantle. Volatiles such as water drastically lower the melting point of the mantle, causing some of the mantle to melt and form magma at depth under the overriding plate. The magma ascends to form an arc of volcanoes parallel to the subduction zone.
The 1946 Aleutian Islands earthquake occurred near the Aleutian Islands, Alaska on April 1, 1946. The shock had a moment magnitude (Mw ) of 8.6, a tsunami magnitude Mt of 9.3, and a surface-wave magnitude (Ms ) of only 7.4, and a maximum Mercalli intensity of VI (Strong). It resulted in 165–173 casualties and over $26 million in damage. The seafloor along the fault was elevated, triggering a Pacific-wide tsunami with multiple destructive waves at heights ranging from 45–138 ft (14–42 m). The tsunami obliterated the Scotch Cap Lighthouse on Unimak Island, Alaska among others, and killed all five lighthouse keepers. Despite the destruction to the Aleutian Island Unimak, the tsunami had almost an imperceptible effect on the Alaskan mainland.
The Kuril–Kamchatka Trench or Kuril Trench is an oceanic trench in the northwest Pacific Ocean. It lies off the southeast coast of Kamchatka and parallels the Kuril Island chain to meet the Japan Trench east of Hokkaido. It extends from a triple junction with the Ulakhan Fault and the Aleutian Trench near the Commander Islands, Russia, in the northeast, to the intersection with the Japan Trench in the southwest.
A triple junction is the point where the boundaries of three tectonic plates meet. At the triple junction each of the three boundaries will be one of three types – a ridge (R), trench (T) or transform fault (F) – and triple junctions can be described according to the types of plate margin that meet at them. Of the ten possible types of triple junctions only a few are stable through time. The meeting of four or more plates is also theoretically possible but junctions will only exist instantaneously.
The Okhotsk Plate is a minor tectonic plate covering the Kamchatka Peninsula, Magadan Oblast, and Sakhalin Island of Russia; Hokkaido, Kantō and Tōhoku regions of Japan; the Sea of Okhotsk, as well as the disputed Kuril Islands. It was formerly considered a part of the North American Plate, but recent studies indicate that it is an independent plate, bounded on the north by the North American Plate. The boundary is a left-lateral moving transform fault, the Ulakhan Fault originating from a triple junction in the Chersky Range. On the east, the plate is bounded by the Pacific Plate at the Kuril–Kamchatka Trench and the Japan Trench, on the south by the Philippine Sea Plate at the Nankai Trough, on the west by the Eurasian Plate, and on the southwest by the Amurian Plate.
Many major earthquakes have occurred in the region of the Kamchatka Peninsula in far eastern Russia. Events in 1737, 1923 and 1952, were megathrust earthquakes and caused tsunamis. There are many more earthquakes and tsunamis originating from the region.
The Aleutian Trench is an oceanic trench along a convergent plate boundary which runs along the southern coastline of Alaska and the Aleutian islands. The trench extends for 3,400 kilometres (2,100 mi) from a triple junction in the west with the Ulakhan Fault and the northern end of the Kuril–Kamchatka Trench, to a junction with the northern end of the Queen Charlotte Fault system in the east. It is classified as a "marginal trench" in the east as it runs along the margin of the continent. The subduction along the trench gives rise to the Aleutian Arc, a volcanic island arc, where it runs through the open sea west of the Alaska Peninsula. As a convergent plate boundary, the trench forms part of the boundary between two tectonic plates. Here, the Pacific Plate is being subducted under the North American Plate at a dip angle of nearly 45°. The rate of closure is 7.5 centimetres (3 in) per year.
The Mendocino Fracture Zone is a fracture zone and transform boundary over 4000 km long, starting off the coast of Cape Mendocino in far northern California. It runs westward from a triple junction with the San Andreas Fault and the Cascadia subduction zone to the southern end of the Gorda Ridge. It continues on west of its junction with the Gorda Ridge, as an inactive remnant section which extends for several hundred miles.
The 1957 Andreanof Islands earthquake occurred at 04:22 local time on March 9 with a moment magnitude estimated between 8.6 and 9.1 and a maximum Modified Mercalli intensity of VIII (Severe). It occurred south of the Andreanof Islands group, which is part of the Aleutian Islands arc. The event occurred along the Aleutian Trench, the convergent plate boundary that separates the Pacific Plate and the North American plates near Alaska. A basin-wide tsunami followed, with effects felt in Alaska and Hawaii, and strong waves recorded across the Pacific rim. Total losses were around $5 million.
The 2006 Kamchatka earthquake occurred on . This shock had a moment magnitude of 7.6 and a maximum Mercalli intensity of X (Extreme). The hypocenter was located near the coast of Koryak Autonomous Okrug at an estimated depth of 22 km, as reported by the International Seismological Centre. This event caused damage in three villages and was followed by a number of large aftershocks. Two M6.6 earthquakes struck on April 29 at 16:58 UTC and again on May 22 at 11:12 UTC. These earthquakes caused no deaths; however, 40 people were reported injured.
The Macquarie Triple Junction is a geologically active tectonic boundary located at 61°30′S161°0′E at which the Indo-Australian Plate, Pacific Plate, and Antarctic Plate collide and interact. The term Triple Junction is given to particular tectonic boundaries at which three separate tectonic plates meet at a specific, singular location. The Macquarie Triple Junction is located on the seafloor of the southern region of the Pacific Ocean, just south of New Zealand. This tectonic boundary was named in respect to the nearby Macquarie Island, which is located southeast of New Zealand.
The Ulakhan Fault is a left-lateral moving transform fault that runs along the boundary between two tectonic plates in northeast Asia, the North American Plate, and the Okhotsk Plate. It runs from a triple junction in the Chersky Range in the west, to another triple junction with the Aleutian Trench and the Kuril Trench in the east. From the offset of dated geomorphological features, a slip rate of 5.3±1.3 mm per year has been measured, consistent with estimates from GPS constrained global plate models. The analysis of fault scarps along the fault zone in the Seymchan Basin suggests that the fault is characterised by occasional large earthquakes.
The Galapagos Triple Junction is a geological area in the eastern Pacific Ocean several hundred miles west of the Galapagos Islands where three tectonic plates - the Cocos Plate, the Nazca Plate and the Pacific Plate - meet. It is an unusual type of triple junction in which the three plates do not meet at a simple intersection. Instead, the junction includes two small microplates, the Galapagos Microplate and the Northern Galapagos Microplate, caught in the junction, turning synchronously with respect to each other and separated by the Hess Deep rift.
The Chile Triple Junction is a geologic triple junction located on the seafloor of the Pacific Ocean off Taitao and Tres Montes Peninsula on the southern coast of Chile. Here three tectonic plates meet: the South American Plate, the Nazca Plate and the Antarctic Plate. This triple junction is unusual in that it consists of a mid-oceanic ridge, the Chile Rise, being subducted under the South American Plate at the Peru–Chile Trench. The Chile Triple Junction is the boundary between the Chilean Rise and the Chilean margin, where the Nazca, Antarctic, and South American plates meet at the trench.
The Shirshov Ridge is located on the eastern border of the Commander Basin below the Kamchatka Peninsula. It extends directly southward for a distance of 750 km toward the Aleutian arc in the eastern part of the Bering Sea.
The Pacific Ocean evolved in the Mesozoic from the Panthalassic Ocean, which had formed when Rodinia rifted apart around 750 Ma. The first ocean floor which is part of the current Pacific Plate began 160 Ma to the west of the central Pacific and subsequently developed into the largest oceanic plate on Earth.
The Aleutian subduction zone is a 2,500 mi (4,000 km) long convergent boundary between the North American Plate and the Pacific Plate, that extends from the Alaska Range to the Kamchatka Peninsula. Here, the Pacific Plate is being subducted underneath the North American Plate and the rate of subduction changes from west to east from 7.5 to 5.1 cm per year. The Aleutian subduction zone includes two prominent features, the Aleutian Arc and the Aleutian Trench. The Aleutian Arc was created via volcanic eruptions from dehydration of the subducting slab at ~100 km depth. The Aleutian Trench is a narrow and deep morphology that occurs between the two converging plates as the subducting slab dives beneath the overriding plate.
On July 17 2017, an earthquake struck near the Komandorski Islands, east of the Kamchatka Peninsula in the Bering Sea at. Although there were no casualties from this earthquake, it was notable for a rare characteristic known as supershear, and is one of the few times a large supershear earthquake has been observed. It was preceded by a few foreshocks months earlier, and aftershocks that continued for nearly six months.
The Chile Ridge, also known as the Chile Rise, is a submarine oceanic ridge formed by the divergent plate boundary between the Nazca Plate and the Antarctic Plate. It extends from the triple junction of the Nazca, Pacific, and Antarctic plates to the Southern coast of Chile. The Chile Ridge is easy to recognize on the map, as the ridge is divided into several segmented fracture zones which are perpendicular to the ridge segments, showing an orthogonal shape toward the spreading direction. The total length of the ridge segments is about 550–600 km.
