By far the most seismically active state in the U.S., Alaska is the site of the second-largest earthquake ever recorded. In 1964, a magnitude 9.2 earthquake in Prince William Sound killed 132 people, more than the recent Loma Prieta and Northridge earthquakes combined. The tsunami generated by the great Alaska earthquake killed people as far south as California. This event inspired the formation of the Alaska Earthquake Information Center.
The Alaska Earthquake Information Center, a member of the Advanced National Seismic System (ANSS), is funded by the State of Alaska, NOAA, and USGS. Located at the Geophysical Institute of the University of Alaska Fairbanks, the Alaska Earthquake Information Center receives data from more than 400 seismic sites. AEIC serves as an integration of all seismic networks within Alaska, also archiving and processing data from the West Coast and Alaska Tsunami Warning Center located in Palmer, Alaska, (~20 sites), and the Alaska Volcano Observatory with offices in Fairbanks and Anchorage (~180 sites). All sites in the network operate with a real-time data acquisition system at the Geophysical Institute. The network is further strengthened by three Incorporated Research Institutions for Seismology (IRIS) sites, at College, Kodiak Island, and Adak, and two ANSS sites at Eagle and Wrangell.
Alaska Earthquake Information Center personnel locate and report about 22,000 earthquakes each year, and advise federal and state officials of each major earthquake's location and size within 30 minutes. In addition, the earthquake catalogs generated by AEIC are fundamental for seismic hazard studies, because they are the most important element in defining the seismic source zones and the level of seismicity.
The population of Alaska is approximately 600,000 and growing. Anchorage, almost totally destroyed in 1964 and rebuilt on unstable soils, is now home to more than 275,000 people. Other cities in Alaska (for example Fairbanks, Valdez, Seward, and Dutch Harbor) have also grown over the years into major population or undustrial centers and face serious earthquake hazards.
The trans-Alaska pipeline, crossing much of the seismically active areas of the state, is a major domestic carrier of U.S. oil and is at risk from a variety of potential earthquake sources, including the Denali Fault (the longest intraplate fault in the country). The largest fishing industry in the country is located in the Aleutian Islands, and is susceptible not only to significant earthquake hazards but also to volcanic eruptions and to tsunamis from both local and distant earthquake sources. Alaska earthquakes are the major source of tsunamis that impact other areas of the U.S. and Pacific rim countries.
Seismic hazards in Alaska come from several sources. The largest earthquakes in the state are caused by subduction of the Pacific plate beneath Alaska. Three of the seven largest earthquakes in the 20th century occurred in Alaska (1957 Aleutian, 1964 Prince William Sound, and 1965 Rat Islands). Although it is generally believed that these great earthquakes are rare, with recurrence times on the order of hundreds of years for an individual segment, five great underthrusting events have occurred in Alaska since 1938. In addition, both the 1986 Andreanof Islands and the 1996 Delarof Islands magnitude 8-class earthquakes reruptured sections of the 1957 zone, even though only 29 and 39 years, respectively, had passed since that great event. In a recent evaluation of the seismic potential in Alaska, researchers indicated that several subduction zone segments may be ready to rupture soon. The Yakataga gap and the region between Kodiak Island and the Shumagin Islands are areas where magnitude 8+ events are expected. A second type of hazard comes from the smaller magnitude 6.8 to 8.0 earthquakes, which occur in many regions of central and southcentral Alaska. These events, while smaller, occur at more frequent intervals, and in locations that cannot always be predicted. On average, Alaska has a magnitude 7.0 or larger earthquake about every two years. Similar in size to recent California earthquakes, these events could cause major damage if they occurred in a populated or strategically sensitive area. A third hazard exists from the many smaller events that often occur near populated areas. While these events are too small to cause widespread damage, they are relatively common and thus pose a continuous threat to urban areas.
The plots below illustrate how many earthquakes were reported each year in Alaska and the Aleutians combined since 1970 (top) and magnitude of the largest recorded earthuqake for that year (bottom).