Background
The first recorded Illinois earthquake is from 1795, when a small earthquake shook the frontier settlement of Kaskaskia. Data from large earthquakes—in May and July 1909, and November 1968—suggest that earthquakes in the area are of moderate magnitude but can be felt over a large geographical area, largely because of the lack of fault lines. The May 1909 Aurora earthquake affected people in an area of 500,000 square miles (1,300,000 km2); the 1968 Illinois earthquake was felt by those living in an area of about 580,000 square miles (1,500,000 km2). Contradicting the idea that the region's earthquakes are felt over a wide area, a 1965 shock was only noticed near Tamms, even though it had the same intensity level (VII) as those of 1909 and 1968. Before 1968, earthquakes had been recorded in 1838, 1857, 1876, 1881, 1882, 1883, 1887, 1891, 1903, 1905, 1912, 1917, 1922, 1934, 1939, 1947, 1953, 1955, and 1958. Since 1968, other earthquakes have occurred in the same region in 1972, 1974, 1984, and 2008.
Read more about this topic: 1968 Illinois Earthquake
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