UTC time | 1964-03-28 03:36 |
---|---|
ISC event | 869809 |
USGS-ANSS | ComCat |
Local date | March 27, 1964 |
Local time | 17:36:16 AKST [lower-alpha 1] |
Duration | 4–5 minutes |
Magnitude | 9.2 Mw , [1] |
Depth | 25 kilometers (16 mi) |
Epicenter | 60°54′29″N147°20′20″W / 60.908°N 147.339°W |
Type | Megathrust |
Areas affected | United States, Canada |
Total damage | $311 million (1964 USD) [$2.94 billion (2022 USD)] |
Max. intensity | XI (Extreme) |
Peak acceleration | ~ 0.18 g [2] |
Tsunami | Major. Run-up of 67 m (220 ft) at Shoup Bay, Alaska. |
Casualties | 131 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. [3] Across south-central Alaska, ground fissures, collapsing structures, and tsunamis resulting from the earthquake caused about 131 deaths. [4]
Lasting four minutes and thirty-eight seconds, the magnitude 9.2 megathrust earthquake remains the most powerful earthquake ever recorded in North America, and the second most powerful earthquake ever recorded in the world since modern seismography began in 1900. 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. [5] Tsunamis also caused damage in Hawaii and Japan. Evidence of motion directly related to the earthquake was also reported from Florida and Texas.
On March 27, 1964, at 5:36 p.m. AKST (March 28, at 3:36 a.m. UTC), [lower-alpha 1] 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 (20.0 km) north of Prince William Sound, 78 miles (126 km) east of Anchorage and 40 miles (64 km) west of Valdez. The focus occurred at a depth of approximately 15.5 mi (24.9 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. [6] Large rockslides were also caused, resulting in great property damage. Vertical displacement of up to 38 feet (12 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 . [7]
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. [8]
Two types of tsunami were produced by this subduction zone earthquake. There was a tectonic tsunami produced in addition to about 20 smaller and local tsunamis. These smaller tsunamis were produced by submarine and subaerial landslides and were responsible for the majority of the tsunami damage. Tsunami waves were noted in over 20 countries, including Peru, New Zealand, Papua New Guinea, Japan, Mexico, and in the continent of Antarctica. The largest tsunami wave was recorded in Shoup Bay, Alaska, with a height of about 220 ft (67 m). [4] [10]
As a result of the earthquake, 131 people are believed to have died: [4] Nine died as a result of the earthquake itself and another 122 died from the subsequent tsunamis all over the world. [11] Five died from the tsunami in Oregon, [12] and 12 died from the tsunami in Crescent City, California. [13] [14]
The quake was a reported XI on the modified Mercalli Intensity scale "indicating major structural damage, and ground fissures and failures". [15] Property damage was estimated at $116 million [4] ($0.84 billion in 2022 dollars). [16]
Most damage occurred in Anchorage, 75 mi (121 km) northwest of the epicenter. Anchorage was not hit by tsunamis, but downtown Anchorage was heavily damaged, and parts of the city built on sandy bluffs overlying "Bootlegger Cove clay" near Cook Inlet, most notably the Turnagain neighborhood, suffered landslide damage. The neighborhood lost 75 houses in the landslide, and the destroyed area has since been turned into Earthquake Park. [17] The Government Hill school suffered from the Government Hill landslide, leaving it in two jagged, broken pieces. Land overlooking the Ship Creek valley near the Alaska Railroad yards also slid, destroying many acres of buildings and city blocks in downtown Anchorage. Most other areas of the city were only moderately damaged. The 60-foot (18 m) concrete control tower at Anchorage International Airport was not engineered to withstand earthquake activity and collapsed, killing William George Taylor, the Federal Aviation Agency air traffic controller on duty in the tower cab at the time the earthquake began. [18]
One house on W. 10th Avenue suffered peripheral damage, but only one block away the recently completed (and still unoccupied) Four Seasons Building on Ninth Avenue collapsed completely, with the concrete elevator shafts sticking up out of the rubble like a seesaw.
The hamlets of Girdwood and Portage, located 30 and 40 mi (48 and 64 km) southeast of central Anchorage on the Turnagain Arm, were destroyed by subsidence and subsequent tidal action. Girdwood was relocated inland and Portage was abandoned. About 20 miles (32 km) of the Seward Highway sank below the high-water mark of Turnagain Arm; the highway and its bridges were raised and rebuilt in 1964–66.
Most coastal towns in the Prince William Sound, Kenai Peninsula, and Kodiak Island areas, especially the major ports of Seward, Whittier and Kodiak were heavily damaged by a combination of seismic activity, subsidence, post-quake tsunamis and/or earthquake-caused fires. Valdez with 32 dead was not totally destroyed, but after three years, the town relocated to higher ground four miles (6.4 km) west of its original site. Some Alaska Native villages, including Chenega and Afognak, were destroyed or damaged. The earthquake caused the ballistic missile detection radar of Clear Air Force Station to go offline for six minutes, the only unscheduled interruption in its operational history. Near Cordova, the Million Dollar Bridge crossing the Copper River also suffered damage, with Span #4 slipping off its pylon and collapsing. The community of Girdwood was also confined to the southern side of the Seward Highway when water rushed into Turnagain Arm and flooded or destroyed any buildings left standing to the north of the highway. Only the ground immediately along the highway and that on the north side of the road dropped, prompting geologists to speculate that Girdwood may rest upon an ancient cliff face covered by thousands of years of sediment and glacial deposits.[ citation needed ]
A 4.5 ft (1.4 m) wave reached Prince Rupert, British Columbia, just south of the Alaska Panhandle, about three hours after the earthquake. The tsunami then reached Tofino, on the exposed west coast of Vancouver Island, and traveled up a fjord to hit Port Alberni twice, washing away 55 homes and damaging 375 others. The towns of Hot Springs Cove, Zeballos, and Amai also saw damage. [19] The damage in British Columbia was estimated at CA$10 million ($86 million in 2021 Canadian dollars or $87 million in 2022 US dollars). [20] [21] [22]
Twelve people were killed by the tsunami in or near Crescent City, California, while four children were killed on the Oregon coast at Beverly Beach State Park. [23] Other coastal towns in the U.S. Pacific Northwest and Hawaii were damaged. Minor damage to boats occurred as far south as Los Angeles. [24] Effects of the earthquake were even noted as far east as Freeport, Texas, where tide gauges recorded waves similar to seismic surface waves. [25] Seiches were detected in wells in countries around the world, including England, Namibia, and Australia. [26]
There were hundreds of aftershocks in the first weeks following the main shock. In the first day alone, eleven major aftershocks were recorded with a magnitude greater than 6.0. Nine more struck over the next three weeks. In all, thousands of aftershocks occurred in the months following the quake, and smaller aftershocks continued to strike the region for more than a year. [24]
Alaska had never experienced a major disaster in a highly populated area before, and had very limited resources for dealing with the effects of such an event. In Anchorage, at the urging of geologist Lidia Selkregg, the City of Anchorage and the Alaska State Housing Authority appointed a team of 40 scientists, including geologists, soil scientists, and engineers, to assess the damage done by the earthquake to the city. [27] The team, called the Engineering and Geological Evaluation Group, was headed by Dr. Ruth A. M. Schmidt, a geology professor at the University of Alaska Anchorage. The team of scientists came into conflict with local developers and downtown business owners who wanted to immediately rebuild; the scientists wanted to identify future dangers to ensure that rebuilt infrastructure would be safe. [28] The team produced a report on May 8, 1964, just a little more than a month after the earthquake. [27] [29]
The United States military, which has a large active presence in Alaska, also stepped in to assist within moments of the end of the quake. The U.S. Army rapidly re-established communications with the lower 48 states, deployed troops to assist the citizens of Anchorage, and dispatched a convoy to Valdez. [30] On the advice of military and civilian leaders, President Lyndon B. Johnson declared all of Alaska a major disaster area the day after the quake. The U.S. Navy and U.S. Coast Guard deployed ships to isolated coastal communities to assist with immediate needs. Bad weather and poor visibility hampered air rescue and observation efforts the day after the quake, but on Sunday the 29th the situation improved and rescue helicopters and observation aircraft were deployed. [30] A military airlift immediately began shipping relief supplies to Alaska, eventually delivering 2,570,000 pounds (1,170,000 kg) of food and other supplies. [31] Broadcast journalist Genie Chance assisted in recovery and relief efforts, staying on the KENI air waves over Anchorage for more than 24 continuous hours as the voice of calm from her temporary post within the Anchorage Public Safety Building. [32] She was effectively designated as the public safety officer by the city's police chief. [32] Chance provided breaking news of the catastrophic events that continued to develop following the magnitude 9.2 earthquake, and she served as the voice of the public safety office, coordinating response efforts, connecting available resources to needs around the community, disseminating information about shelters and prepared food rations, passing messages of well-being between loved ones, and helping to reunite families. [33]
In the longer term, the U.S. Army Corps of Engineers led the effort to rebuild roads, clear debris, and establish new townsites for communities that had been completely destroyed, at a cost of $110 million. [31] The West Coast and Alaska Tsunami Warning Center was formed as a direct response to the disaster. Federal disaster relief funds paid for reconstruction as well as financially supporting the devastated infrastructure of Alaska's government, spending hundreds of millions of dollars that helped keep Alaska financially solvent until the discovery of massive oil deposits at Prudhoe Bay. At the order of the U.S. Defense Department, the Alaska National Guard founded the Alaska Division of Emergency Services to respond to any future disasters. [30]
Alaska is a non-contiguous U.S. state on the northwest extremity of North America. It borders British Columbia and Yukon in Canada to the east and it shares a western maritime border in the Bering Strait with Russia's Chukotka Autonomous Okrug. The Chukchi and Beaufort Seas of the Arctic Ocean lie to the north and the Pacific Ocean lies to the south. Technically a semi-exclave of the U.S., Alaska is the largest exclave in the world.
Valdez is a city in the Chugach Census Area in the U.S. state of Alaska. According to the 2020 US Census, the population of the city is 3,985, up from 3,976 in 2010. It is the third most populated city in Alaska's Unorganized Borough.
Prince William Sound is a sound off the Gulf of Alaska on the south coast of the U.S. state of Alaska. It is located on the east side of the Kenai Peninsula. Its largest port is Valdez, at the southern terminus of the Trans-Alaska Pipeline System. Other settlements on the sound, which contains numerous small islands, include Cordova and Whittier plus the Alaska native villages of Chenega and Tatitlek.
Cook Inlet stretches 180 miles (290 km) from the Gulf of Alaska to Anchorage in south-central Alaska. Cook Inlet branches into the Knik Arm and Turnagain Arm at its northern end, almost surrounding Anchorage. On its southern end, it merges with Shelikof Strait, Stevenson Entrance, Kennedy Entrance and Chugach Passage.
Girdwood is a resort town within the southern extent of the Municipality of Anchorage in the U.S. state of Alaska. Located near the end of the Turnagain Arm of Cook Inlet, Girdwood lies in a valley in the southwestern Chugach Mountains, surrounded by seven glaciers feeding into a number of creeks, which either converge within the valley or empty directly into the arm. Girdwood is typically accessed by the Seward Highway, with the main line of the Alaska Railroad paralleling the highway. By road distance, most of the community lies within 35 to 40 miles of Downtown Anchorage. The 2019 American Community Survey estimates a population of 1,742 in the valley.
The Seward Highway is a highway in the U.S. state of Alaska that extends 125 miles (201 km) from Seward to Anchorage. It was completed in 1951 and runs through the scenic Kenai Peninsula, Chugach National Forest, Turnagain Arm, and Kenai Mountains. The Seward Highway is numbered Alaska Route 9 (AK-9) for the first 37 miles (60 km) from Seward to the Sterling Highway and AK-1 for the remaining distance to Anchorage. At the junction with the Sterling Highway, AK-1 turns west towards Sterling and Homer. About eight miles (13 km) of the Seward Highway leading into Anchorage is built to freeway standards. In Anchorage, the Seward Highway terminates at an intersection with 5th Avenue, which AK-1 is routed to, and which then leads to the Glenn Highway freeway.
The 1946 Aleutian Islands earthquake occurred near the Aleutian Islands, Alaska on April 1, 1946. The shock measured 8.6, Mt 9.3 or 7.4. It had a maximum Mercalli intensity of VI (Strong). It resulted in 165–173 casualties and over US $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 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 history of Alaska dates back to the Upper Paleolithic period, when foraging groups crossed the Bering land bridge into what is now western Alaska. At the time of European contact by the Russian explorers, the area was populated by Alaska Native groups. The name "Alaska" derives from the Aleut word Alaxsxaq, meaning "mainland".
After congress approved the completion of the Alaska Railroad from Seward to Fairbanks in 1914, it was decided that a new town should be built as a port and rail hub along the route. The decision was made to develop a site near Ship Creek on Cook Inlet. Survey parties visited the area in 1914 and researched possible routes for the rails and options for siting the new town. Anchorage was originally settled as a tent city near the mouth of Ship Creek in 1915, and a planned townsite was platted alongside the bluff to the south. Anchorage was mostly a company town for the Alaska Railroad for its first several decades of existence.
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 Municipality of Anchorage is the largest city in the U.S. state of Alaska by population. With a population of 291,247 at the 2020 census, it contains nearly 40 percent of the state's population, and has more people than all of Northern Canada and Greenland combined. The Anchorage metropolitan area, which includes Anchorage and the neighboring Matanuska-Susitna Borough, had a population of 398,328 in 2020, accounting for more than half the state's population. At 1,706 sq mi (4,420 km2) of land area, the city is the fourth-largest by area in the United States and larger than the smallest state, Rhode Island, which has 1,212 sq mi (3,140 km2).
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On November 30, 2018, at 8:29 a.m. AKST (17:29 UTC), a magnitude 7.1 earthquake hit Anchorage in South Central Alaska. The earthquake's epicenter was near Point Mackenzie, about 10 miles (16 km) north of Anchorage, and occurred at a depth of 29 miles (47 km). It was followed six minutes later by a magnitude 5.7 aftershock centered 2.5 miles (4.0 km) north-northwest of the municipality. The earthquake could be felt as far away as Fairbanks.
The 1907 Sumatra earthquake occurred on January 4 at 05:19:12 UTC. The estimated magnitude is 7.5–8.0 Ms, with an epicentre close to Simeulue, off Sumatra. It triggered a widespread and damaging tsunami that caused at least 2,188 deaths. The low observed intensity compared to the size of the tsunami has led to its interpretation as a tsunami earthquake. Higher levels of shaking observed on Nias are attributed to a large aftershock, less than an hour later. The tsunami gave rise to the S'mong legend, which is credited with saving many lives during the 2004 earthquake.
An earthquake occurred off the coast of the Alaska Peninsula on July 28, 2021, at 10:15 p.m. local time. The large megathrust earthquake had a moment magnitude of 8.2 according to the United States Geological Survey (USGS). A tsunami warning was issued by the National Oceanic and Atmospheric Administration (NOAA) but later cancelled. The mainshock was followed by a number of aftershocks, including three that were of magnitude 5.9, 6.1 and 6.9 respectively.
The 1843 Nias earthquake off the northern coast of Sumatra, Indonesia caused severe damage when it triggered a tsunami along the coastline. The earthquake with a moment magnitude (Mw ) of 7.8 lasted nine minutes, collapsing many homes in Sumatra and Nias. It was assigned a maximum modified Mercalli intensity of XI (Extreme).
The 1979 Saint Elias earthquake occurred near noon local time on the 28th of February. It measured Mw 7.4–7.6. Though the maximum recorded Modified Mercalli intensity was VII, damage was minimal and there were no casualties due to the remoteness of the faulting. The epicenter lies near the Alaskan border between America and Canada.