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Home , 1964 Alaska earthquake, Aleutian Trench, George Plafker

The 1964 Great and —A Modern Perspective and Enduring Legacies

Introduction Nation except for Connecticut, Delaware, and Most of the population of Alaska and its major The magnitude 9.2 Great Alaska Rhode Island—registered the earthquake. It transportation routes, ports, and infrastructure Earthquake, which struck south-central Alaska was so large that it caused the entire Earth to lie near the eastern segment of the Aleutian at 5:36 p.m. on Friday, March 27, 1964, is the ring like a bell: vibrations that were among that ruptured in the 1964 earthquake. largest recorded earthquake in U.S. history the first of their kind ever recorded by modern Although the Great Alaska Earthquake was and the second-largest earthquake recorded instruments. The Great Alaska Earthquake tragic because of the loss of life and property, with modern instruments. The earthquake spawned thousands of lesser aftershocks it provided a wealth of data about - was felt throughout most of mainland and hundreds of damaging , zone and the hazards they pose. Alaska, as far west as Dutch Harbor in submarine slumps, and other ground failures. The leap in scientific understanding that the Aleutian Islands 800 miles away from Alaska’s largest city, Anchorage, located followed the 1964 earthquake has led to Anchorage, and at Seattle, , west of the rupture, sustained heavy major breakthroughs in earth science research more than 1,200 miles to the southeast of property damage. Tsunamis produced by the worldwide over the past half century. This the fault rupture, where the Space Needle earthquake resulted in deaths and damage as fact sheet commemorates the Great Alaska swayed perceptibly. The earthquake caused far away as and . Altogether Earthquake and examines the advances in rivers, lakes, and other waterways to slosh as the earthquake and subsequent tsunamis knowledge and technology that have helped to far away as the coasts of and Louisiana. caused 129 fatalities and an estimated $2.3 improve earthquake preparation and response Water-level recorders in 47 states—the entire billion in property losses (in 2013 dollars). both in Alaska and around the world.

Damage to the caused by the 1964 Great Alaska Earthquake. Photograph by the U.S. Army.

U.S. Department of the Interior Fact Sheet 2014–3018 U.S. Geological Survey March 2014 Scientific Impact of the Great Alaska Earthquake

Support for the Theory of , it descends, or At first, geologists did not know how subducts, into the Earth’s mantle along the such a huge earthquake could have happened, . Subduction zones like because the prevailing theories of the day could southern Alaska’s occur throughout the not explain such a large movement. So they world, and the was examined the earthquake within the framework the first to be generally understood by earth damage to the waterfront area of Kodiak, of a new theory, plate tectonics, which scientists as having occurred on a subduction Alaska. USGS photograph by . proposed that the crust of the Earth consists zone interface: the slip was along the gently of about a dozen or so major sections, or dipping boundary, or “megathrust fault,” tsunamis produced by the 1964 Great Alaska plates, that sit on top of the hot mantle below between the denser downgoing oceanic plate Earthquake was one of the first events to and slowly move past each other or collide. and the lighter overriding continental plate. demonstrate to scientists that an earthquake Compelling evidence for this theory is that Since 1964, subduction zones have been may cause changes of seafloor depth that most earthquakes occur near the boundaries recognized elsewhere, including Indonesia, generate transoceanic tsunamis. of these plates, and the plates’ movements , and , where great earthquakes The 1964 earthquake was giant because through geologic time help to explain many have also occurred during the past 60 years. of the large area of the fault that slipped of the landforms and processes that we observe The understanding gained from the 1964 during the earthquake and the large amount on Earth. Great Alaska Earthquake provided the of slip, or relative motion, between opposite Earth scientists now recognize that the geological framework for assessing the sides of the earthquake fault. Current 1964 Great Alaska Earthquake resulted from earthquake and tsunami hazards estimates of the average slip along the plate convergence: where the Pacific at all convergent margins megathrust fault during the 1964 earthquake Plate is being overridden by the N around the world. are in the range of 30 feet, with some patches Anchorage For example, the that slipped as much as 60 feet! Turnagain Heights Government Hill

Map of southern Alaska showing the epicenter of the 1964 Great Alaska Earthquake (red star), caused when the Pacific

Plate lurched northward 0 10 underneath the North MILES Anchorage American Plate. There was extensive damage NORTH AMERICAN to coastal towns and Kenai infrastructure throughout PLATE Peninsula Whittier Valdez the region, particularly Cook Prince in Anchorage, Seward, Inlet Seward William Whittier, and Valdez. Sound Widespread uplift occurred Chenega seaward of Montague Delta and the , SUBSIDENCE Island while subsidence occurred Middleton Island inland as a result of the Kodiak Kodiak UPLIFT AND magnitude 9.2 earthquake. Island In 1964, there were no SUBSURFACE instruments in Alaska RUPTURE capable of recording the earthquake, but now there ch is an extensive network of en N Tr stations (yellow squares) tian Aleu that monitor the seismically ALASKA active plate boundary PACIFIC OCEAN along the Aleutian Trench. (detailed map) 0 100 Modern seismic stations MILES Volcanoes Movement of plate Seismogram of 1964 Great Alaska Earthquake from station in Weston, Massachusetts. Each line is 30 minutes. Image courtesy of IRIS Data Management System.

Observation and Explanation of In areas experiencing initial sudden and in the Kodiak Island area, show that the Earthquake Ground Deformation subsidence, such as and much last 1964-type earthquake may have occurred Geologists from the U.S. Geological of Kodiak Island, coastal forests and peaty 880 years ago and that the average interval Survey (USGS) were the first earth scientists marsh deposits dropped below sea level and between great earthquakes is about 535 years. to respond to the devastated region, and they were killed by the sudden inundation by Middleton Island, located offshore mapped land-level changes resulting from salt water. These drowned forests become southern Alaska, was uplifted about 10 feet the 1964 earthquake all along the coast of buried by marine silt, and, in some places, by the 1964 earthquake, and a new wave- southern Alaska. They were astonished to by tsunami sand deposits. During the gradual cut terrace was formed. The observation of find that the earthquake was accompanied by uplift that follows, salt-water-tolerant peat this new landform led to subsequent USGS vertical shifts of the Earth’s surface over an eventually accumulates on the marine silt, study of a series of five other wave-cut area two-thirds the size of California. Parts of and new forests grow on the peat. In other terraces that were first noticed on the island the coast sank, or subsided, as much as 8 feet, places, such as the Copper River Delta, in 1933 but were not originally recognized and other parts rose by as much as 38 feet. In located closer to the Aleutian Trench, as earthquake-related features. Geologists addition, geodetic surveys showed that much sudden uplift occurs first, followed by slow realized that each terrace had been formed by of coastal Alaska moved seaward at least submergence between earthquakes. uplift during a great 1964-type earthquake. 50 feet. The uplift and subsidence data from Sediment cores collected through these Radiocarbon dating of fossil driftwood the 1964 earthquake have been repeatedly cyclic uplift/subsidence deposits have yielded from beach deposits on these older terraces used to test models of how subduction zones an unprecedented 5,600-year-long record of showed that the repeat times for these prior rupture during great earthquakes and to great earthquakes along the southern Alaska earthquakes ranged from 400 to 1,200 years, calculate how much the plates shifted along coast. In the Copper River Delta, the cores with an average of 800 years. Since the 1964 the fault plane at depth. show evidence of 9 prehistoric earthquakes, earthquake, similar wave-cut terraces have It is now recognized that major implying an average interval of about 600 been recognized and used in other subduction subduction-zone earthquakes produce a years between 1964-type great earthquakes in zones to better assess the hazards and pattern of uplift of the coastline above the southern Alaska. Other studies to the west of earthquake recurrence intervals associated shallowest and most seaward part of a the Copper River Delta, in the Turnagain Arm with them. rupture, and that subsidence of the coastline occurs farther inland from the rupture. This The movement of the Pacific Plate northward beneath the North American Plate resulted in pattern gradually reverses over a period of subsidence in some areas and uplift in others. Whale Bay, on (inset), rose decades to centuries as continuing plate nearly 10 feet, but a roadway on the Kenai Peninsula sank beneath sea level and was washed out. motion restores the Earth’s Both USGS photographs by George Plafker. surface to its pre-earthquake state. This cyclic pattern was first revealed in the studies following the 1964 earthquake. Recognizing Hazards due to Movement on Secondary Faults The 1964 Great Alaska Earthquake demonstrated that secondary faults that spread out or splay upward from the main rupture plane can accommodate much of the horizontal and vertical movement One span of the Million Dollar Bridge in the Copper River Delta slipped off its pier, associated with the sudden plate motion. and other spans shifted on their piers These splay faults can locally uplift the due to liquefaction of soils during the seafloor, causing the water above to be strong ground shaking of the Great Alaska displaced and creating a tsunami. The Earthquake. In other places, railroad hazards posed by secondary splay faulting tracks buckled and were torn from their can be severe because, although localized, ties (inset). USGS photographs by R. the uplifts and tsunamis produced by Kachadoorian and M.G. Bonilla (inset). the 1964 earthquake were greater than those generated by displacement in the Increased Understanding of Liquefaction subduction zone itself. These secondary railroad bridges were destroyed when ruptures were commonly located closer Catastrophic soil failure in the their pilings and piers sank or spread to shore, reducing the travel and warning Alaskan and Niigata, Japan, earthquakes apart because the underlying soils flowed. times of the waves. After the 1964 in 1964 provided a new insight that Parts of the railroad were out of service earthquake, vertical uplifts of 36 feet were liquefaction of sandy soils caused by for nearly six months. The 1964 Alaskan mapped along splay faults on Montague earthquake shaking poses a major threat and Japanese earthquakes prompted Island, and vertical uplifts along related to the stability of engineered structures. extensive government-funded research by faults were inferred to extend as far south During strong earthquake shaking, geotechnical engineers in both countries as Kodiak Island. These uplifts produced geologically young, water-saturated sandy on the physics of liquefaction and large tsunamis on the Kenai Peninsula deposits can act like a liquid, causing implications for structural stability. Their near Seward and on Kodiak Island. Such them to flow downhill and to lose their findings led to the development of field- secondary faulting is likely also responsible ability to support manmade structures based methods to determine liquefaction for the tsunami disaster in Aceh, Indonesia, during the shaking. More than $30 million potential of coarse-grained soils; these during the 2004 Great Aceh-Andaman in damage, from both liquefaction and methods are used around the world by civil Earthquake. tsunamis, was sustained by the federally engineers to ensure the safety of structures owned . Many important in earthquake-prone areas.

The waterfront of Whittier, Alaska, was heavily damaged by tsunamis generated by underwater landslides. Whittier was an important all-weather port for both governmental and industrial groups, but the dock facilities were destroyed and were inoperable for months following the earthquake, tsunamis, and a major at a fuel-tank farm. Left photograph, aerial view of the waterfront during the fire; right photograph, railroad tracks and tanks that were mangled by the ground shaking and subsequent landslides. Increased Understanding of Earthquake last ruptured in 2002 in a magnitude 7.9 estuaries of the U.S. west coast sustained Hazards in Alaska and Elsewhere earthquake (see USGS Fact Sheet 014-03, millions of dollars in damage. Such http://pubs.usgs.gov/fs/2003/fs014-03/). The destruction from such a faraway earthquake The understanding of the characteristics plate tectonic picture is more complicated in provided motivation for the development of subduction zones, and the earthquakes eastern Alaska, where variations in crustal of West Coast/Alaska Tsunami Warning and tsunamis such zones produce, dates thickness cause the Pacific Plate to descend Center (now called the National Tsunami largely from the 1964 Great Alaska at a shallower angle than in the west. This Warning Center), operated by the National Earthquake. Geologists are thus able shallower angle increases earthquake Oceanic and Atmospheric Administration, to identify the hazards posed by great hazards in southern Alaska because it causes which uses earthquake data supplied by the subduction-zone earthquakes in areas where the great earthquakes to occur closer to USGS. Tsunami warning centers can now they have not occurred recently, or even in the Earth’s surface and, therefore, places send alerts within minutes of an earthquake historical times, like the Cascadia subduction population centers at higher risk. that has the potential for generating a zone (along the coast of , tsunami. Although this system works well Washington, Oregon, and northern Tsunami Hazard Assessments and for tsunamis that travel across the ocean, it is California). Identifying these hazards in Warnings too slow to provide significant warning time advance will help reduce losses in future for tsunamis generated by local splay-fault great earthquakes. An important lesson from the ruptures and submarine landslides. For these Since the 1964 Great Alaska 1964 Great Alaska Earthquake, and local tsunamis, the strong shaking produced Earthquake, scientists at the USGS and from subsequent great subduction-zone by the earthquake serves as the tsunami elsewhere have used Global Positioning earthquakes, is that tsunami damage can warning. Tsunami risk is also mitigated by System (GPS) receivers to accurately be much more widespread than shaking mapping tsunami inundation zones, planning measure the rate at which the Pacific Plate damage, and it can occur thousands of evacuation routes, educating coastal is converging with southern Alaska, as well miles from the causative earthquake. The communities and their visitors, constructing as the rate of motion along crustal faults orientation of the 1964 fault rupture directed tsunami-resistant infrastructure, and creating in southern Alaska. These measurements the tsunami southeastward toward the earthquake monitoring and tsunami warning show that the Pacific Plate is sliding beneath Washington, Oregon, and California systems and centers, all of which have been southern Alaska at an average rate of 2.3 coastline, where it caused extensive completed and are regularly updated for inches per year. The plates move in a flooding and damaged the U.S. west coast and other areas where stick-slip motion with strain accumulating harbors. Sixteen people tsunamis may occur. on the when it died and the is stuck, and strain is suddenly released coasts and when the subduction zone slips, causing an N earthquake. GPS measurements also show that this plate convergence compresses the crust of southern Alaska, pushing it out to the west along faults with horizontal (lateral) offsets such as on the Denali Fault, which

The 1964 Great Alaska Earthquake occurred where the cold, dense Pacific Plate is moving north, pushed into and under the more buoyant North American Plate. EXPLANATION The Yakutat Plate (labeled YAK) is Fault sections ruptured in historical record: Fairweather a fragment of oceanic crust, like the Fault (1958), Aleutian Megathrust Fault and Patton Bay Pacific Plate, and is being dragged along Fault Zone (PBFZ; 1964), Denali and Totschunda Faults (2002). Barb on upper plate into the subduction zone on top of the Pacific Plate, inhibiting the movement of the downgoing Faults with prehistorical ruptures. Barb on upper plate plate. The cross sections show how the Pacific Movement of plates and Yakutat Plates together are more buoyant and Volcano subduct at a shallower angle than the Pacific Plate 1964 epicenter and surface projection of rupture patch in alone. subduction zone Effects of the Earthquake Enduring Legacies Survivors of the 1964 Alaska In 1964, no instruments capable of earthquake will never forget the strong recording the strong ground motions produced shaking that lasted for as much as four by the Great Alaska Earthquake were located and a half minutes when a 580-mile in southern Alaska. Since then, in cooperation section of the fault plane ruptured. with the State of Alaska, the USGS has installed assess- One Anchorage resident recorded his an extensive earthquake-monitoring network as ment and observations throughout the earthquake, part of the Advanced National Seismic System. evaluation describing shaking at his residence that (For more information, see Fact Sheet 075–00, of earthquake lasted for four minutes. The long duration http://pubs.usgs.gov/fs/2000/fs075-00/.) hazards in of the movement led to significant ground Such recordings provide data seismologists Alaska. failures, slumping, landsliding, and need to assess shaking hazards during future The establishment of the USGS liquefaction in the Anchorage area. Massive earthquakes, and are used to prepare the USGS National Center for Earthquake Research in landslides were triggered in and near National Maps (http://pubs. 1964 brought together the USGS earthquake Anchorage and Government usgs.gov/fs/2008/3017/) and ShakeMaps, expertise into a single point of focus, and Hill, as well as in the Turnagain Heights which show the distribution and severity of it became a cornerstone of the USGS residential area. Water and gas mains, as earthquake ground motion. Using ShakeMaps Earthquake Hazards Program, in turn a major well as sewer, telephone, and electrical and a comprehensive worldwide population element of the National Earthquake Hazards systems were disrupted throughout database, the USGS now makes rapid estimates Reduction Program (NEHRP). Under the Turnagain Heights owing to landslides. of the expected fatalities and economic losses direction of the NEHRP, the USGS protects In southern Alaska, where the loss of from large earthquakes around the globe using life and property by monitoring earthquakes life was largest, 70 percent of the fatalities a system called PAGER, or Prompt Assessment nationally and internationally, making resulted from tsunamis generated by of Global Earthquakes for Response (see seismic-hazard assessments used in building massive submarine landslides that occurred Fact Sheet 2010–3036, http://pubs.usgs.gov/ codes and for other purposes, conducting on steep slopes of the seafloor. Because of fs/2010/3036/). The ground-motion data research in earthquake occurrence and physics, the proximity of many of these submarine from more recent events are also used by the and performing outreach and education on landslides to coastal communities, the engineering community to design buildings and earthquake phenomena and hazards. tsunamis they created reached landfall other structures to resist earthquake shaking, within a few minutes of the start of ground helping to minimize loss of life and property. shaking and inundated some areas as much The scientific observations and interpre- Additional Resources as 170 feet above sea level. The coastal tations of the 1964 Great Alaska Earthquake The Great Alaska Earthquake and Tsunami, communities of Whittier, Valdez, and are preserved in publications for use by future USGS Earthquake Hazards Program: Seward were hit particularly hard by these generations. The USGS published the results of http://earthquake.usgs.gov/earthquakes/ locally caused tsunamis. Chenega, a small its comprehensive study of the 1964 earthquake alaska1964/ village in Prince William Sound, lost 23 in a series of six Professional Papers (avail- people—a third of its population—when able at http://earthquake.usgs.gov/earthquakes/ Earthquake Preparedness Guide, Alaska a 65-foot wave arrived about four minutes alaska1964/) that document geologic, seismo- Earthquake Information Center: after the earthquake. These sobering logic, and hydrologic observations following the http://www.aeic.alaska.edu/html_docs/next- facts show that residents of any coastal earthquake, as well as earthquake- and tsunami- bigeq.html community need to immediately head related damage to infrastructure and Alaska “Magnitude 9.2,” video by the USGS: to higher ground when they feel seismic communities. The data continue to be used on http://www.youtube.com/watch?v=jvl-4IWjH shaking. a daily basis for land-use planning as well as Xo&list=UUeXH8GZyV3sVqAr45AvupOA &feature=share&index=3

Thomas M. Brocher, John R. Filson, Gary S. Fuis, Peter J. Haeussler, Thomas L. Holzer, George Plafker, and J. Luke Blair

Edited by Claire M. Landowski Graphic design by Jeanne S. DiLeo

Earthquake Science Center U.S. Geological Survey Menlo Park, CA 94025 Cape Cleare on Montague Island was uplifted 33 feet during the 1964 Great Alaska Earthquake, creating the new http://earthquake.usgs.gov; terrace shown here. The white coating on the rocks—about a quarter of a mile wide—is the remains of marine Earthquake Information Hotline: (650) 329-4085 microorganisms that were desiccated when the seafloor was uplifted out of the water. On the mountains in the This Fact Sheet and any updates to it are background, light gray patches are landslides triggered by ground shaking. Photo at top right shows ground failure available online at and damage to homes in the Turnagain Heights area of Anchorage, Alaska. USGS photographs by George Plafker. http://pubs.usgs.gov/fs/2014/3018/ ISSN 2327–6932 (online); ISSN 2327–6916 (print) Printed on recycled paper http://dx.doi.org/10.3133/fs20143018