From Ohio History Central
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| caption = C.A. Dillingham wrote this letter to Isaac Jones in Maine while staying in Cincinnati in April 1812. He writes about the earthquake of 1811, which was centered in New Madrid, Missouri and felt throughout the Midwest including in Ohio. Dillingham also discusses conflicts with American Indians. The letter is four pages and measures 7.5" x 12.5" (19.05 x 31.75 cm).
<p>Ohio has recorded at least 200 earthquakes above 2.0-magnitude since the earliest record in 1776. Most of these events have been small, in the 2 to 3 magnitude range, but at least 15 earthquakes centered in the state have caused damage. The largest earthquake in Ohio occurred on March 9, 1937, in western Ohio in the Shelby
-Auglaize Counties area. This earthquake followed a smaller one on March 2, and is estimated to have had a magnitude of 5.4. Considerable damage occurred in Anna and surrounding communities, including damage to nearly every chimney in Anna, cracks and wall separation in the school, rotation of cemetery monuments, changes in water wells, and other minor -to -moderate damage. The Anna school was condemned and torn down.</p><p>Ohio’s earthquakes are concentrated in two primary zones, but also occur with less frequency and intensity in other areas of the state. The Western Ohio Seismic Zone includes Allen, Auglaize, Mercer, and Shelby Counties and was particularly active in the 1930’s but still has periodic earthquakes. These earthquakes occur at depths of about three miles along faults associated with a Precambrian failed rift zone. The rift zone trends northwest from Champaign County and into Indiana.</p><p>The Northeastern Ohio Seismic Zone includes a broad area from eastern Cuyahoga County east to the Pennsylvania border and south to the vicinity of Akron. Most activity in this area has been concentrated in Lake County and beneath Lake Erie offshore from Lake and Ashtabula Counties. A sequence of earthquakes centered at Ashtabula, beginning in 1987, is interpreted to have been induced by fluids from a deep injection well. The largest earthquake in this zone occurred on January 31, 1986 in southern Lake County. This 5.0-magnitude event was felt throughout a multistate area and caused minor to moderate damage. A 4.5-magnitude earthquake at Ashtabula in 2001 caused minor damage. An extensive linear feature in deep Precambrian rocks, known as the Akron Magnetic Boundary, is thought to be responsible for some of these earthquakes. The causes of earthquakes in this region are poorly understood at present.</p>
<p>Small earthquakes have occurred in a broad area of southern Ohio. A few of them have caused minor damage. A small number of minor earthquakes have been scattered across some other areas as well.</p>
[[Category:Natural History Geology]]