1979 Saint Elias earthquake

Earthquake in Alaska 1979 Saint Elias earthquake Alaska 1979-02-28 21:27:06 670396 usp0000z2a 1979 02 28 yes 12:27:06 AKST w y 7.5 15.0 km on Chugach Mountains and Saint Elias Mountains, 60.642 -141.593 region:AK_type:event inline,title Thrust Alaska, Yukon Limited 7 0.16 g Yes None The 1979 Saint Elias earthquake affected southeastern Alaska at 12:27 AKST on 28 February. The thrust-faulting w y 7.5 earthquake had an epicenter in the east of the Chugach Mountains. The earthquake occurred along an uncertain plate boundary where previous large earthquakes have occurred. Though the maximum recorded Modified Mercalli intensity was VII (Very strong), damage was minimal and there were no casualties due to the remoteness of the faulting. The shaking was widespread and the damage also extended across the border to parts of Yukon, Canada. Tectonic setting In the Saint Elias region, the North American plate and Yakutat Terrane converge with the Pacific plate at rates of 45–50 mm on/yr. The Pacific plate undergoes subduction beneath North America along the Aleutian Trench west of the Saint Elias area, while strike-slip faulting between the two plates occurs to the east on the Queen Charlotte Fault. Faults in the Saint Elias region exhibit thrust and reverse slip while there is localised strike-slip deformation evident in some earthquake fault plane solutions.Doser 2012 In the area of the epicenter, several surface faults exist that may have slipped during the earthquake.Lahr Plafker Stephens Foglean 1979 The Saint Elias area represents a transition zone between the convergent and strike-slip plate motions. This area was also the location of a series of large earthquakes in 1899. Aside from the earthquake of 1979, no other major earthquakes have occurred in the Saint Elias region since 1899, and the 1964 and 1958 earthquakes ruptured adjacent segments of the plate boundary. This part of the plate boundary, dubbed the Yakataga Gap, extends 250 km across, where great earthquakes of magnitude 8.0 or larger have a recurrence interval of 80 years. Only a section of this gap ruptured during the 1979 earthquake.McCann Pérez Sykes 1980 Earthquake The earthquake, which occurred at a shallow depth of 15.0 km, was the largest to strike the continental United States since 1964. It measured 7.5 on the moment magnitude scale (w), while on the surface-wave magnitude scale (s), measured between 7.1 and 7.7.Lahr Hasegawa Boatwright 1980 The earthquake occurred beneath the Chugach and Saint Elias ranges and was observed by 50 seismic stations in Southeast Alaska.Lahr Hasegawa Boatwright 1980 Geology Beneath the Saint Elias range, the Pacific plate and possibly the Yakutat Block subduct at a rate of 5.3 cm annually. The earthquake occurred in this region, known as Yakataga, where a seismic gap was previously identified. This gap represented a section of the subduction zone where no large earthquakes have occurred since the 1899 Yakutat Bay earthquakes. Adjacent sections of the subduction zone ruptured during the 1964 and the 1958 earthquakes.Estabrook Nábělek Lerner-Lam 1992Tape Lomax 2022 While the 1979 earthquake occurred on this seismic gap, it did not fully rupture the entirety of it. Therefore, a possible seismic gap remains west of the 1979 and east of the 1964 ruptures.Lahr Plafker Stephens Foglean 1979 A focal mechanism analysis suggest shallow thrust and strike-slip faulting was responsible for the earthquake. The rupture initiated on a thrust fault that dipped to the north and propagated east-southeast on the fault before transitioning onto a separate northeast-dipping dextral fault.Estabrook Nábělek Lerner-Lam 1992 The distribution of aftershocks in the area suggest a maximum rupture dimension of approximately 65 km by 80 km and extending southeast of the epicenter. Part of the rupture extended beneath Canada's Yukon Territory.Lahr Hasegawa Boatwright 1980Doser 2012 There was no foreshock activity,Lahr Hasegawa Boatwright 1980 and the largest aftershock measured w 5.2. The largest aftershocks displayed a variety of focal mechanisms involving thrust, strike-slip, and normal faulting.Doser 2012 The earthquake caused 0.4–1.0 m on of movement on the fault; only a portion (10–30%) of the total slip accumulated since the 1899 events.Estabrook Nábělek Lerner-Lam 1992 Impact The earthquake occurred in the sparsely populated and glaciated Chugach Range. It was felt the strongest, VII (Very strong) on the Mercalli intensity scale, at Icy Bay Lumber Camp, 73 km on away, where a logging truck bounced violently.Brockman Espinosa Michael 1988 A March 2 aerial reconnaissance flight did not find major damage within 40 km on of the epicenter.Lahr Plafker Stephens Foglean 1979 Damage to drywall and plaster, and displaced furniture, were observed in Mendenhall, Haines, Border City, Juneau, and Cape Yakataga. At Border City, a wooden building situated on permafrost was displaced at its base. Two fractures appeared in the concrete floor of a restaurant in Yakutat. Wallboards cracked at Valdez Airport, though the building did not sustain structural damage. Many people in the airport reported difficulty standing up. Likewise, at Juneau Airport, passengers disembarking a plane struggled to stand and a heavy desk in the terminal was shaken.Stover Von Hake 1984 In Yukon Territory, fractures appeared in the local school wall at Beaver Creek. A building in Burwash Landing sustained cracks while cracked plasters appeared in a lodge at Destruction Bay.Stover Von Hake 1984 The shaking was widespread, with people reportedly feeling the earthquake 1,200 km on away,Brockman Espinosa Michael 1988 and shaking being felt over a distance of 500,000 sqkm on.Stover Von Hake 1984 In Iowa, some wells reported water level fluctuations of up to 1.42 ft on.Logel 1980 Three accelerographs located within 250 km of the epicenter recorded strong ground motion data from the earthquake. A peak horizontal acceleration of 0.16 g recorded in Icy Bay, 74 km away, was the highest recorded ground motion. Yakutat recorded peak horizontal acceleration of 0.09 g. The Alyeska Pipeline Service Company also recorded digital ground motion data in Valdez using their accelerographs, with peak horizontal acceleration there being 0.013 g.Lahr Stephens 1983 At Sitka, a 6 in tsunami was recorded while a 2 in tsunami occurred in Yakutat. An erroneous entry that was included in a 1979 report stated that a 30 cm tsunami was recorded. Many snow avalanches were observed aerially to the south and southeast of the epicentral region.Lahr Plafker Stephens Foglean 1979 On the Saint Elias range, between Mount Huxley and Mount Augusta, severe avalanches travelled more than 1 mi away from the north face of the range. Multiple large (6–106 m3) rock avalanches fell from slopes near the Seward Glacier. Many large (3–5 km2) landslides also occurred.Bessette-Kirton Coe 2020 The mainshock and aftershock distribution on land suggest the tsunami was triggered by a small and local landslide. After a couple of months, earthquake activity died down and resembled the regional stress field before the mainshock. See also List of earthquakes in 1979 List of earthquakes in the United States List of earthquakes in Alaska List of earthquakes in Canada References OB 670396 Media release Kelly Don Aftershocks Continue From Major Alaska Quake 1979 https://learningfromearthquakes.org/images/earthquakes/1979_Mt_St_Elias_AK/USA_AK_MtStElias_Aftershock_May79.pdf United States Geological Survey Significant Earthquake Database https://www.ngdc.noaa.gov/hazel/view/hazards/earthquake/event-more-info/6457 National Geophysical Data Center / World Data Service (NGDC/WDS) National Geophysical Data Center, NOAA 10.7289/V5TD9V7K 1972 Data Set Global Historical Tsunami Database National Geophysical Data Center / World Data Service (NGDC/WDS) https://www.ngdc.noaa.gov/hazel/view/hazards/tsunami/event-more-info/2111 NOAA National Centers for Environmental Information Data Set M 7.1 – 113 km SE of McCarthy, Alaska 1979 usp0000z2a M 5.4 – 127 km SE of McCarthy, Alaska 1979 usp0000z39 Sources Brockman Stanley R. Espinosa A. F. Michael J. A. 1988 Catalog of intensities and magnitudes for earthquakes in Alaska and the Aleutian Islands, 1786–1981 10.3133/b1840 https://dggs.alaska.gov/webpubs/usgs/b/text/b1840.pdf Bulletin 1840 United States Geological Survey Doser Diane I. Revisiting the 1979 St. Elias, Alaska, Aftershock Sequence and Its Regional Significance Bulletin of the Seismological Society of America 2012 102 6 2392–2404 10.1785/0120120007 2012BuSSA.102.2392D Estabrook Charles H. Nábělek John L. Lerner-Lam Arthur L. Tectonic model of the Pacific-North American Plate Boundary in the Gulf of Alaska from broadband analysis of the 1979 St. Elias, Alaska, earthquake and its aftershocks Journal of Geophysical Research 10 May 1992 97 B5 6587–6612 10.1029/92JB00131 1992JGR....97.6587E https://agupubs.onlinelibrary.wiley.com/doi/10.1029/92JB00131 11 December 2022 subscription Bessette-Kirton Erin K. Coe Jeffrey A. 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Earthquake Activity and Ground Shaking in and Along the Eastern Gulf of Alaska 1983 Interior Department, Minerals Management Service BOEM Environmental Studies https://espis.boem.gov/final%20reports/1454.pdf Logel John The effects of the February 28, 1979 Alaskan earthquake on ground water levels in Iowa Bulletin of the Seismological Society of America 1 October 1980 70 5 1667–1668 10.1785/BSSA0700051667 1980BuSSA..70.1667L https://pubs.geoscienceworld.org/ssa/bssa/article-abstract/70/5/1667/118098/The-effects-of-the-February-28-1979-Alaskan 11 December 2022 subscription McCann William R. Pérez Omar J. Sykes Lynn R. Science Yakataga Gap, Alaska: Seismic History and Earthquake Potential March 21, 1980 207 4437 1309–1314 10.1126/science.207.4437.1309 1980Sci...207.1309M 128624810 https://www.science.org/doi/10.1126/science.207.4437.1309 11 December 2022 subscription United States Earthquakes, 1979 1984 https://pubs.usgs.gov/of/1984/0979/report.pdf Stover Carl W. Von Hake Carl A. Open-File Report United States Geological Survey Open-File Report 84–979 10.3133/ofr84979 180 Tape Carl Lomax Anthony Aftershock Regions of Aleutian-Alaska Megathrust Earthquakes, 1938–2021 Journal of Geophysical Research: Solid Earth 2022 127 7 10.1029/2022JB024336 2022JGRB..12724336T 249857173 free Category:1979 earthquakes Category:Earthquakes in Alaska Category:Earthquakes in Canada Category:Tsunamis in the United States Category:1979 in Alaska Category:February 1979 in the United States Category:1970s tsunamis Category:1979 in Yukon Category:Disasters in Yukon Category:Natural history of Yukon