The 1925 Montana (Clarkston Valley) earthquake occurred at 17:21:12 MDT on 27 June in Montana, with the epicenter being located near Townsend. The earthquake had a magnitude of 6.9 in the surface-wave magnitude scale. A maximum intensity of IX (Violent) was observed. Serious damage was reported near the epicenter. 3 hours after the mainshock, a strong aftershock was recorded with an unknown magnitude that also caused damage.[2]

Tectonic setting

The epicenter area, Clarkston Valley is a valley surrounded by mountains of severely folded Mesozoic and older rocks and floored with tertiary lake beds and recent alluvium. Physiographic evidences indicate that the Clarkston Valley is a structural depression on the east by a fault of post-Miocene age. Presumably the origin of the earthquake was on this fault at a considerable depth below the surface. In the neighborhood of Deer Lodge several faults of apparently small extent that trend northwestward are mapped by the geologists of the Anaconda Copper Mining. Their age and displacement are not known. In the hills west of Missouri River is an overthrust fault, called the Lombard overthrust, that extends from a point north of Three Forks northeastward for 13 miles. Its trace crosses Horseshoe Bend about a mile west of Lombard.[2]

Earthquake

The earthquake struck at 6:21 in the evening local time (June 28 at 01:21 UTC)[3] with the epicenter being located right near Townsend. The earthquake had an intensity of IX (Violent), and was felt in Oregon, Idaho, Wyoming, Washington in the United States and British Columbia, Saskatchewan, Alberta in Canada.[2] Despite the intensity, there were no deaths since back then the area was sparsely populated and the property damage didn't exceed US$ 150,000.[4]

Impact

A damaged church in Three Forks, Montana following the earthquake

A school in Manhattan was damaged beyond repair as well as other schools in Willow Creek, Bozeman and Radersburg being seriously damaged, along with many brick, stone and cement buildings including a church at Three Forks, Logan and a court house in White Sulphur Springs.[2] Many buildings were damaged, pavements were cracked, windows were broken and chimneys toppled as a result of the earthquake.[5] The shaking triggered landslides along the Missouri River which blocked railroad traffic for several weeks.[6]

Casualties

Even though there were no deaths from the earthquake, at least two people were injured including a woman who broke her leg while rushing out of her home.[5]

See also

References

  1. ^ ISC (2016), ISC-GEM Global Instrumental Earthquake Catalogue (1900–2012), Version 3.0, International Seismological Centre
  2. ^ a b c d Pardee, J. T. (1927). "Montana Earthquake of June 27, 1925" (PDF). Retrieved January 9, 2022.
  3. ^ "Montana Shaken by Earthquakes over Wide Area", AP report in Sunday World-Herald (Omaha NE), June 28, 1925, p.1 ("Nearly two-thirds of the state of Montana was shaken vigorously by two series of earthquake shocks early tonight, the first at 6:23 o'clock and the second at 7:07.")
  4. ^ "Clarkson Valley Earthquake – Montana – June 27, 1925". devastatingdisasters.com. Devastating Disasters. Retrieved January 9, 2022.
  5. ^ a b "1925 – Clarkston Valley, MT – M 6¾". University of Utah. Retrieved January 9, 2022.
  6. ^ "1925 Clarkston Valley Earthquake". shakeout.org. The Great Montana Shakeout. Retrieved January 9, 2022.
Allikas: https://en.wikipedia.org/wiki/1925_Townsend_earthquake
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