Tuesday, October 26, 2010

Wyoming Earthquakes like no other...

Earthquake History

The first earthquake known to originate in Wyoming occurred on June 25, 1894, near Casper. Dishes fell to the floor, and a number of people were thrown from their beds (MM V). The Platte River was thick with mud, apparently stirred up by the tremor. On November 14, 1897, another shock caused considerable damage to the Grand Central Hotel at Casper. A 2- to 4-inch crack extended from the third to the first story (MM VI-VII). Frightened citizens dashed into the streets.
A moderate earthquake on July 25, 1910, shook houses (MM V) and was felt in mine shafts at Rock Springs. On May 8, 1915, a shock was felt (MM V) in the north-central part of Yellowstone National Park. Thirteen minor shocks were felt (MM V) at Kelly during the March 23 - April 12, 1923, period. A strong earthquake with noticeable rumbling (MM V) occurred at Big Horn on November 17, 1925. The tremor was felt in Johnson and Sheridan Counties, an area of approximately 7800 square kilometers. Mine props near Thermopolis were loosened during an earthquake on February 13, 1928, and later became tight (MM V). Bumping and trembling sensations were reported at Thermopolis; there were sounds noted before the shock was felt. The earthquake was also felt at Crosby, Gebo, Kirby, Owl Creek, and Worland. The felt area covered about 7800 km square.
One brick building, at Grover was cracked from a June 12, 1930, tremor (MM VI). Also, a concrete swimming pool about 5 kilometers northwest of town was cracked. Minor aftershocks continued sporadically until November 16. Another long series of moderate shocks occurred in the Yellowstone Park area from August 24 to December 22, 1930. Dishes fell, and other light damage occurred (MM V). Cracked plaster and broken dishes were also reported from a January 26, 1932, earthquake south of Yellowstone Park. At Grovemont, Jackson, Kelly, and Moran, people were awakened (MM V-VI) by the shock. The telephone line westward into Idaho was put out of order, presumably by the earthquake. The tremor was also felt at DuBois and Lander. There were a number of aftershocks felt at Jackson on January 26 and 27.
Persons vacated office buildings at Lander during a moderate earthquake on November 23, 1934. Slight damage occurred (MM V). The tremor was strong at Atlantic City and was also felt at Riverton and Rock Springs. The total felt area included approximately 21,000 km square. Two brick chimneys were cracked (MM VI), and small objects were moved near the south entrance to Yellowstone Park on January 14, 1936. The shock was also felt at Moran, where beds rocked from the 9:40 PM jolt. Another earthquake was felt by everyone (MM V) at the West Thumb Ranger Station in Yellowstone Park on August 5, 1942. Windows and dishes rattled from the tremor.
The region south of Yellowstone Park was disturbed again on February 23, 1948. Intensity VI effects were observed at Jackson, Moran, and Wilson; windows, doors, and dishes rattled, hanging objects swung, buildings creaked, and so forth. At Moran, a piano and a bed shifted. The shock was felt over an area of approximately 3900 km square.
Medicine Bow National Forest in southeastern Wyoming was jolted by an earthquake on January 20, 1954. Furnishings shifted and windows rattled (MM V) at Albany; buildings shook at Centennial and Laramie. It was also strongly felt at Foxpark and Jelm, where a lighter aftershock was felt about 5 hours after the 1:50 PM tremor. Felt reports were received from Cowdrey, Colo., and Tie Siding, Wyo.; the total area affected was about 5200 km square. Yellowstone Park was shaken again on July 4, 1954. Many residents at Mammoth were awakened (MM V) by a 12:40 AM tremor. Another shock at 9:32 AM caused buildings to creak and small objects to shift; also, windows, doors, and dishes rattled loudly. Four or five minor shocks with the same type of effects (MM V) were felt in the Old Faithful area on April 28, 1958.
The magnitude 7.1 earthquake centered near Hebgen Lake, Montana, occurred just before midnight on August 17, 1959. At least 28 persons died, and over \$11 million damage resulted. In Yellowstone National Park, about 18,000 people were vacationing. No one was killed or badly injured, although huge boulders smashed down onto roads and buildings in the park were shaken noticeably and did sustain some minor damage. The well-known thermal features of the park were disrupted by the tremor. Old Faithful's eruptions slowed slightly from an average 61-minute cycle to 65 minutes. Other geysers changed eruption times, new ones began to erupt, and many bubbling springs burst into violent activity. The earthquake was felt over one-half of Wyoming, an area included within a diagonal running from southwest to northeast. Minor felt reports were received from Casper and from Hat Creek, near the Nebraska State line.
Numerous aftershocks continued in Yellowstone Park through 1963. Maximum intensities were V and VI, and the felt areas generally were small. Dates and descriptions of these events are contained in Earthquake History of the United States Many additional shocks of intensity IV or less are listed in the annual United States Earthquakes publications.
On February 25, 1963, a magnitude 4.3 earthquake jarred windows, doors, and dishes at Fort Washakie (MM V). The rapid 2- to 3-second shock shifted a bed in one home. The shock was also felt at Lander. The area around Van Tassell, near the Nebraska State line, felt a moderate earthquake on March 27, 1964. Doors and dishes rattled and furniture vibrated (MM V). Thunderlike noises were heard. The tremor was also felt in parts of western Nebraska and South Dakota. The same general area felt a magnitude 4.5 shock on August 21, 1964. Intensity V effects were observed at Keeline, Lost Springs, and Lusk; it was also felt at Jay Em, Lance Creek, and Node.
Slight damage (MM V) occurred at Thermopolis from a magnitude 4.1 earthquake on December 8, 1972. The ceiling was cracked at a rest home; the concrete floor of a lumber yard building settled about 7.6 centimeters. The shock was felt in much of the surrounding area. On April 21, 1973, the area between Jeffrey City and Lander was shaken by a magnitude 4.8 earthquake. Many residents were awakened by the 11:07 PM tremor (MM V).
Yellowstone National Park experienced another strong shock on August 30, 1974. Intensity V effects were reported at Norris, Old Faithful, and West Yellowstone. Numerous additional small tremors were recorded on the seismograph at the Old Faithful Visitor Center. Another swarm of minor tremors was recorded on October 17. This increased seismic activity culminated on June 30, 1975, with a magnitude 6.4 earthquake. Rockslides and landslides stopped or hindered traffic on many roads in the park. Some geysers were affected (MM VII). Telephone service was out for several hours. The shock was felt over approximately 50,000 square kilometers of Wyoming, Montana, Idaho, and scattered places in Nevada, South Dakota, Utah, and Washington. Several aftershocks occurred in the area through July. Still another series of earthquakes originated in the northwestern corner of Yellowstone Park during December 1976. The largest of these shocks, magnitude 5.1, occurred on December 9. Intensity V effects were reported at Canyon Village; intensity IV effects, at Madison Junction and Mammoth Hot Springs; and intensity III effects, at the Old Faithful Visitor Center.
A small earthquake, magnitude 2.3, occurred near Rawlins on January 27, 1976. The tremor knocked a lamp off a table and pictures from a wall (MM V) according to a press report. No other felt reports were received.
From Earthquake Information Bulletin, Volume 10, Number 4, July-August 1978, by Carl von Hake. 


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