1983 Borah Peak earthquake
 Borah Peak with fault scarp seen near base of tan hill in foreground |
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| Date | October 28, 1983 - 14:06 UTC 8:06 am MDT (UTC-6) |
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| Magnitude | 7.3 6.9 - (Richter) |
| Depth | 6-10 mi. (12-20 km) |
| Epicenter | 44°02′46″N 113°53′13″W / 44.046°N 113.887°W Lost River Range central Idaho |
| Countries or regions |  United States |
| Max. intensity | MM IX |
| Tsunami | No |
| Landslides | Yes |
| Casualties | 2 child fatalities |
The 1983 Borah Peak earthquake occurred on October 28, 1983, in the Lost River Range at Borah Peak in central Idaho, United States. The most significant earthquake recorded in the state, it occurred on a Friday morning at 8:06 am MDT. The earthquake was a magnitude 7.3, and 6.9 on the Richter scale. [1]
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[edit] Geography
Along with being the largest, it is almost the most damaging earthquake as well. Two children were killed by falling masonry while walking to school in Challis, about 120 miles (200 km) northeast of Boise, the state's capital. $12.5 million in damage took place in the Challis-Mackay region. Maximum Mercalli scale intensity IX damage was decided upon, as a result of extreme surface faulting, while vibrational damage was at a Mercalli intensity of VI to VII.[2]
The rupture caused clear surface faulting a 21 mile (34 km) long northwest moving zone of fresh scarps and ground rupture was present on a slope of the Lost River Range. Extensive breakage occurred along a 5 mile (8 km) zone between West Spring and Cedar Creek; ground surface was literally "shattered" into tilted blocks, each meters in width. These scarps were as broad as 330 feet (100 m).[2]
[edit] Damage
The Challis-Mackay region experienced rather thorough damage, with 11 commercial buildings and 39 homes with major damage; while another 200 houses were damaged, minor to moderately. Mackay in particular, about 50 miles (80 km) southeast of Challis, experienced the most severe damage. Most of the city's large buildings on its Main Street were damaged, to some extent; eight of these buildings were deemed condemned and closed down. Most of these buildings were built from materials such as brick, concrete block, and stone, each varying.[2]
[edit] Artesian fountains
Near Chilly Buttes of Thousand Springs Valley, a series of artesian fountains erupted immediately after the main shock of the 1983 Borah Peak earthquake. Water gushed from these fountains forming small craters and depositing fluvial aprons of light-colored sandy sediment around each crater.
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Fault scarps that outline the trough (graben) produced during the 1983 Borah Peak earthquake. Photo taken near Willow Creek at Doublespring Pass Road. (USGS Photo, 1983)
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Crater caused by an artesian fountain that flowed during the 1983 Borah Peak earthquake. (USGS Photo, 1983)
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Another view of an artesian fountain triggered by the Borah Peak earthquake. (USGS Photo, 1983)
[edit] References
- ^ Idaho Geological Survey - Geo note 05 - Borah Peak earthquake - prepared 1986-02 - accessed 2010-03-30
- ^ a b c "Historic Earthquakes: Borah Peak, Idaho". USGS. 2008-07-16. http://earthquake.usgs.gov/regional/states/events/1983_10_28.php. Retrieved 2008-12-06.
