The Pacific plate subducting under the North American plate, leads to increased faulting. This subduction began in the Early Cretaceous and continues into the present day. Within and near the Aleutian Island arc and depending on the location, there is thrust faulting, strike-slip faulting, and normal faulting. These result in an increased amount of seismic activity. Earthquakes can reach magnitudes between 7-8.5.[3]
Trench morphology
The north side of the trench slopes 3°–4° and the south side 1°–4°.[4] The deepest part of the Aleutian trench has been measured at 7,822 metres (25,663 ft) at 51.21°N, 174.83°E.,[5] located about 145 kilometres (90 mi) SSW of
Buldir Island.
Center pressure: 10,762 pounds per square inch (732.3 atm; 74.20 MPa).[6] Variations in total magnetic intensity (residual) of more than 600 γ (600
nanoteslas) were found in the center of the trench and more than 1100 γ on the southern flank.[7]
Associated seismicity
The
subduction of the
Pacific Plate below the
North American Plate along the Aleutian Trench is associated with numerous earthquakes. Several of these earthquakes are notable for their size and/or associated
tsunamis.
June 10–11,
1585 Aleutian Islands earthquake: A misdated tsunami legend in the Sanriku coast of Japan was dismissed and inferred to be from a vaguely–documented tsunami event in Miyagi Prefecture on June 11, 1585. Evidence of a large tsunami in the 16th century was also discovered in the Hawaiian Islands in the form of deposits. Oral records from the native residents described a tsunami-like event killing many people. Modelling of a tsunami from an earthquake of 9.25 Mw in the Aleutian Islands proved consistent with the descriptions and
paleotsunami evidences.
April 1,
1946 Aleutian Islands earthquake: This
magnitude 8.6 earthquake occurred offshore
Unimak Island,[8] and caused only minor damage on land. However, the shaking generated a tsunami which killed 5 US Coast Guard personnel on the island, destroying the
Scotch Cap Light, and causing damage on other Aleutian Islands and North and South America. In
Hilo, Hawaii, the tsunami killed 159 and caused extensive damage.
March 27,
1964 Alaska earthquake: Lasting four minutes and thirty-eight seconds, the magnitude 9.2
megathrust earthquake remains the most powerful earthquake recorded in North American history, and the second most powerful earthquake recorded in world history. Nine hundred and seventy kilometres (600 mi) of fault ruptured at once and moved up to 18 metres (60 ft), releasing about 500 years of stress buildup. Most damage directly from the earthquake was in
Anchorage, Alaska and the surrounding areas; a Pacific-wide tsunami caused destruction as far away as
Crescent City, California. The death toll from both earthquake and tsunami was 131.
May 7, 1986 Andreanof Islands earthquake: This
magnitude 7.9 earthquake caused damage on
Adak Island and
Atka Island. The resultant tsunami was recorded throughout the Pacific.[11]
On June 23, 2014, a
7.9 quake occurred near Little Sitkin Island, Alaska.