1983 Borah Peak earthquake
Encyclopedia
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
.
, 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.
The rupture caused clear surface faulting a 21 mile (34 km) long northwest moving zone of fresh scarp
s 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).
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.
Lost River Range
The Lost River Range is a group of high mountains located in central Idaho, in the northwestern United States. It runs southeast for approximately 75 miles from the Salmon River near the community of Challis to the Snake River Valley near Arco...
at Borah Peak
Borah Peak
Borah Peak is the highest mountain in the U.S. state of Idaho. It is located in the central section of the Lost River Range, within the Challis National Forest in eastern Custer County. The peak is named for William Borah , a prominent U.S...
in central
Central Idaho
Central Idaho is a geographical term located northeast of Boise and southeast of Lewiston in the U.S. state of Idaho . It is dominated by federal lands administered by the United States Forest Service and the Bureau of Land Management. Idaho's tallest mountain, Borah Peak, is located in this region...
Idaho
Idaho
Idaho is a state in the Rocky Mountain area of the United States. The state's largest city and capital is Boise. Residents are called "Idahoans". Idaho was admitted to the Union on July 3, 1890, as the 43rd state....
, United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
. The most significant earthquake
Earthquake
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...
recorded in the state, it occurred on a Friday morning at 8:06 am MDT
Mountain Time Zone
The Mountain Time Zone of North America keeps time by subtracting seven hours from Coordinated Universal Time, also known as Greenwich Mean Time, during the shortest days of autumn and winter , and by subtracting six hours during daylight saving time in the spring, summer, and early autumn...
. The earthquake was a magnitude
Moment magnitude scale
The moment magnitude scale is used by seismologists to measure the size of earthquakes in terms of the energy released. The magnitude is based on the seismic moment of the earthquake, which is equal to the rigidity of the Earth multiplied by the average amount of slip on the fault and the size of...
7.3, and 6.9 on the Richter scale
Richter magnitude scale
The expression Richter magnitude scale refers to a number of ways to assign a single number to quantify the energy contained in an earthquake....
.
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 ChallisChallis, Idaho
Challis is a city in Custer County, Idaho, United States. The population was 909 at the 2000 census. The city is the county seat of Custer County.-History:...
, about 120 miles (200 km) northeast of Boise
Boise, Idaho
Boise is the capital and most populous city of the U.S. state of Idaho, as well as the county seat of Ada County. Located on the Boise River, it anchors the Boise City-Nampa metropolitan area and is the largest city between Salt Lake City, Utah and Portland, Oregon.As of the 2010 Census Bureau,...
, 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.
The rupture caused clear surface faulting a 21 mile (34 km) long northwest moving zone of fresh scarp
Fault scarp
A fault scarp is the topographic expression of faulting attributed to the displacement of the land surface by movement along faults. They are exhibited either by differential movement and subsequent erosion along an old inactive geologic fault , or by a movement on a recent active fault...
s and ground rupture was present on a slope of the Lost River Range
Lost River Range
The Lost River Range is a group of high mountains located in central Idaho, in the northwestern United States. It runs southeast for approximately 75 miles from the Salmon River near the community of Challis to the Snake River Valley near Arco...
. 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).
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. MackayMackay, Idaho
Mackay is a city in Custer County, Idaho, United States. The population was 566 at the 2000 census.-Geography:Mackay is located at , at an elevation of 5,905 feet ....
in particular, about 50 miles (80 km) southeast of Challis
Challis, Idaho
Challis is a city in Custer County, Idaho, United States. The population was 909 at the 2000 census. The city is the county seat of Custer County.-History:...
, 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.