Английская Википедия:1979 Saint Elias earthquake

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Шаблон:Short description Шаблон:Infobox earthquake

The 1979 Saint Elias earthquake occurred near noon local time on the 28th of February. It measured Шаблон:M7.4–7.6. 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 epicenter lies near the Alaskan border between America and Canada.

Tectonic setting

Southern Alaska lies along the eastern portion of the Aleutian Trench, where the Pacific plate subducts underneath the North American plate, though in the area near the earthquake the zone begins to transition to continental underthrusting. Most of the activity in the area occurs to the west, such as the devastating 1964 Alaska earthquake where there is a clear subduction zone. However, near the earthquake there exists a complex zone of deformation as faulting transitions from a subduction zone to nearly pure strike slip faulting. In this transition zone, the continental Yakutat block impedes subduction, but allows for shallow thrusting events such as this one. A seismic gap exists here; it last ruptured in the 1899 Yakutat Bay earthquakes.Шаблон:SfnШаблон:Sfn

Earthquake

The earthquake struck near the border between Yukon and Alaska at around noon local time on February the 28th.Шаблон:Sfn According to the United States Geological Survey, the surface-wave magnitude (Шаблон:M) was 7.1,[1] however it was also reported as high as 7.7 Шаблон:M.Шаблон:Sfn The moment magnitude (Шаблон:M) was evaluated to be 7.4–7.6.[2][3] It occurred at a shallow depth of Шаблон:Convert which is a relatively normal depth for an area of continental underthrusting.[1]

It may have partially ruptured the Yakataga seismic gap that had previously ruptured during the large sequences of earthquakes in 1899.Шаблон:Sfn The tectonic setting around the epicenter region is described as complex.Шаблон:Sfn The region is the junction between the strike-slip Fairweather, Denali, Totschunda and Duke River faults in the east. Meanwhile, to the west, subduction is ongoing at the Aleutian Trench.Шаблон:Sfn

Shallow thrust faulting as well as strike-slip faulting was responsible for the earthquake, possibly along a Décollement.Шаблон:Sfn The source fault had an estimated dip angle of 15° to the northwest, with slip between Шаблон:Convert.Шаблон:SfnШаблон:Sfn The earthquake accommodated around 30% of the accumulated stress build up since the 1899 events in the area.Шаблон:Sfn There is little consensus on the main fault(s) responsible for the earthquake, but the most likely culprits are the Chugach-Saint Elias, Coal Glacier, Chaix Hills, Malaspina, or Esker Creek faults.[4]Шаблон:Sfn No foreshock sequence was observed.Шаблон:Sfn There were surprisingly few aftershocks for an event of the size, with the largest only reaching magnitude 5.4.[1] The aftershock distribution may indicate that the Malaspina fault was involved in the rupture of this event.Шаблон:Sfn The largest aftershocks displayed a variety of focal mechanisms, with some being thrust, some being strike-slip, and others as a result of normal faulting.Шаблон:Sfn

Tsunami and landslides

At Sitka, a Шаблон:Cvt tsunami was recorded. The tsunami measured Шаблон:Cvt in Yakutat. An erroneous entry that was included in a 1979 report stated a Шаблон:Cvt tsunami occurred. Many snow avalanches were aerially observed to the south and south-east of the epicentral region.[4] Multiple large (6-10 Mm³) rock avalanches fell from slopes near the Seward Glacier, and multiple large (3–5 km2) landslides were triggered.Шаблон:Sfn The mainshock and aftershock distribution on land suggest the tsunami was triggered by a small and local landslide.[5]

Damage

The earthquake struck the eastern part of the Chugach Mountains, a sparsely populated region consisting of glaciers.[6] It was felt the strongest (VII on the Mercalli intensity scale[7]) at Icy Bay Lumber Camp Шаблон:Convert away, where a logging truck bounced to its side.Шаблон:Sfn Many people reported difficulties in standing up. Some minor damage was reported in Border City, Cape Yakataga, the Juneau area, Valdez, and Yakutat. In Canada's Yukon Province, damage occurred in Beaver Creek, Burwash Landing, Destruction Bay, and Kluane Lake Fishing Camp.[6] The shaking was widespread, with people reportedly feeling MMI III (Weak) shaking Шаблон:Convert away,Шаблон:Sfn and shaking being felt over a distance of Шаблон:Convert.Шаблон:Sfn In Iowa, some wells reported water level fluctuations of up to Шаблон:Convert.Шаблон:Sfn

See also

References

Шаблон:Reflist

Sources Шаблон:Refbegin

Шаблон:Refend

Шаблон:Earthquakes in 1979 Шаблон:Earthquakes in Alaska

Партнерские ресурсы
Криптовалюты
Магазины
Хостинг
Разное

  1. ↑ 1,0 1,1 1,2 Ошибка цитирования Неверный тег <ref>; для сносок usgs не указан текст
  2. ↑ Ошибка цитирования Неверный тег <ref>; для сносок GCMT не указан текст
  3. ↑ Ошибка цитирования Неверный тег <ref>; для сносок usgs3 не указан текст
  4. ↑ 4,0 4,1 Ошибка цитирования Неверный тег <ref>; для сносок usgs2 не указан текст
  5. ↑ Ошибка цитирования Неверный тег <ref>; для сносок TE не указан текст
  6. ↑ 6,0 6,1 Ошибка цитирования Неверный тег <ref>; для сносок NGDC не указан текст
  7. ↑ Ошибка цитирования Неверный тег <ref>; для сносок ISC не указан текст
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