1964 Alaska earthquake

1964 Alaska earthquake
AlaskaQuake-FourthAve.jpg
Fourth Avenue in Anchorage, Alaska, looking east from near Barrow Street. The southern edge of one of several landslides in Anchorage, this one covered an area of over a dozen blocks, including five blocks along the north side of Fourth Avenue. Most of the area was razed and made an urban renewal district.
Good Friday Earthquake 1964 03 28 loc.jpg
UTC time1964-03-28 03:36
869809
USGS-ComCat
Local dateMarch 27, 1964 (1964-03-27)
Local time17:36:16 AKST
Duration4–5 minutes.
Magnitude9.2 Mw,[1] 6.7 mb  (ISC)
Depth25 kilometers (16 mi)
Epicenter60°54′29″N 147°20′20″W / 60°54′29″N 147°20′20″W / 60.908; -147.339
TypeMegathrust
Areas affectedUnited States, Canada
Total damage$311 million (1964 USD)
Max. intensityXI (Extreme)
Peak acceleration0.18 g
TsunamiMajor. Run-up of 67 m (220 ft) at Shoup Bay, Alaska.
Casualties131 killed

The 1964 Alaskan earthquake, also known as the Great Alaskan earthquake and Good Friday earthquake, occurred at 5:36 PM AKST on Good Friday, March 27.[2] Across south-central Alaska, ground fissures, collapsing structures, and tsunamis resulting from the earthquake caused about 131 deaths.[3]

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. Six hundred miles (970 km) of fault ruptured at once and moved up to 60 ft (18 m), releasing about 500 years of stress buildup. Soil liquefaction, fissures, landslides, and other ground failures caused major structural damage in several communities and much damage to property. Anchorage sustained great destruction or damage to many inadequately earthquake-engineered houses, buildings, and infrastructure (paved streets, sidewalks, water and sewer mains, electrical systems, and other man-made equipment), particularly in the several landslide zones along Knik Arm. Two hundred miles (320 km) southwest, some areas near Kodiak were permanently raised by 30 feet (9 m). Southeast of Anchorage, areas around the head of Turnagain Arm near Girdwood and Portage dropped as much as 8 feet (2.4 m), requiring reconstruction and fill to raise the Seward Highway above the new high tide mark.

In Prince William Sound, Port Valdez suffered a massive underwater landslide, resulting in the deaths of 32 people between the collapse of the Valdez city harbor and docks, and inside the ship that was docked there at the time. Nearby, a 27-foot (8.2 m) tsunami destroyed the village of Chenega, killing 23 of the 68 people who lived there; survivors out-ran the wave, climbing to high ground. Post-quake tsunamis severely affected Whittier, Seward, Kodiak, and other Alaskan communities, as well as people and property in British Columbia, Washington, Oregon, and California.[4] Tsunamis also caused damage in Hawaii and Japan. Evidence of motion directly related to the earthquake was also reported from Florida and Texas.

Geology

On March 27, 1964, at 5:36 p.m. AKST (3:36 a.m. UTC), a fault between the Pacific and North American plates ruptured near College Fjord in Prince William Sound. The epicenter of the earthquake was 12.4 mi (20 km) north of Prince William Sound, 78 miles (125 km) east of Anchorage and 40 miles (64 km) west of Valdez. The focus occurred at a depth of approximately 15.5 mi (25 km). Ocean floor shifts created large tsunamis (up to 220 feet (67 m) in height), which resulted in many of the deaths and much of the property damage.[5] Large rockslides were also caused, resulting in great property damage. Vertical displacement of up to 38 feet (11.5 m) occurred, affecting an area of 100,000 square miles (260,000 km2) within Alaska.

Studies of ground motion have led to a peak ground acceleration estimate of 0.14–0.18 g.[6]

The Alaska earthquake was a subduction zone (megathrust) earthquake, caused by an oceanic plate sinking under a continental plate. The fault responsible was the Aleutian Megathrust, a reverse fault caused by a compressional force. This caused much of the uneven ground which is the result of ground shifted to the opposite elevation. [7]

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