Iowa has experienced only minor earthquake activity since the United States obtained control of the State under the Louisiana Purchase in 1803. It was not until 1857, 11 years after Statehood, that the present boundaries were drawn up. As a territory, Iowa had included Minnesota and parts of North and South Dakota.
The great New Madrid Missouri, earthquakes, of 1811 - 1812 were the first reported felt in Iowa. The absence of historical records from the territory, prevents an accurate assessment of the actual effects from these earthquakes.
The Sioux City area was shaken by an earthquake on July 3, 1858. Press reports described the tremors as of sufficient force to shake pictures and crockery from their places. On October 9, 1872, Sioux City again experienced a moderately strong earthquake. Intensity V effects were noted near the center of the disturbance, with the total felt areas estimated to be about 3,000 square miles, including adjoining portions of the Dakotas.
On November 15, 1877, another earthquake was felt throughout Iowa and eastern Nebraska, and in parts of Missouri, Kansas, the Dakotas, Wisconsin, and Minnesota. The strongest effects were noted at Columbus, Lincoln, North Platte, and Omaha, Nebraska. However, large cracks in the walls of several buildings in Sioux City resulted from this shock. A second earthquake was reported 45 minutes later.
An intensity V shock was reported at Keokuk on April 13, 1905. Buildings were shaken, but no serious damage was done. The shock was apparently local in character. Riverton, Iowa, felt intensity V effects from an earthquake on March 1, 1935, which was centered in southeastern Nebraska.
Two other events are significant. On October 20, 1965, an earthquake in eastern Missouri affected a 160,000 square mile area, and reportedly caused large cracks in a house foundation at Indianola, Iowa. Intensity V effects were also noted at Ottumwa. The earthquake of November 9, 1968, centered in Illinois, produced Intensity V effects in Iowa at Albia, Bloomfield, Burlington, Clinton, Elkader, Muscatine, and Walpello. The earthquake was not felt in the northwestern quadrant of the State. The 1895 tremor, centered near Charleston, Missouri, did some slight damage to a few chimneys in Keokuk. This earthquake was felt noticeably in the southeastern part of Iowa, and probably felt over the whole State.
Abridged from Earthquake Information Bulletin, Volume 4, Number 5, September - October 1972.
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