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]
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 ofBuldir 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 (600nanoteslas) were found in the center of the trench and more than 1100 γ on the southern flank.[7]
Thesubduction of thePacific plate below theNorth American plate along the Aleutian Trench is associated with numerous earthquakes. Several of these earthquakes are notable for their size and/or associatedtsunamis.
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 andpaleotsunami evidences.
April 1,1946 Aleutian Islands earthquake: Thismagnitude 8.6 earthquake occurred offshoreUnimak 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 theScotch Cap Light, and causing damage on other Aleutian Islands and North and South America. InHilo, Hawaii, the tsunami killed 159 and caused extensive damage.
March 27,1964 Alaska earthquake: Lasting four minutes and thirty-eight seconds, the magnitude 9.2megathrust 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 inAnchorage, Alaska and the surrounding areas; a Pacific-wide tsunami caused destruction as far away asCrescent City, California. The death toll from both earthquake and tsunami was 131.
May 7, 1986 Andreanof Islands earthquake: Thismagnitude 7.9 earthquake caused damage onAdak Island andAtka Island. The resultant tsunami was recorded throughout the Pacific.[11]
On June 23, 2014, a7.9 quake occurred near Little Sitkin Island, Alaska.
