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SMALL EARTHQUAKE IN MERCER COUNTY OHIO
Origin Time: January 30, 2004, 12:10:04.14 UTC (7:10 a.m. EST)
Location: 40.67º N -84.62º W
Magnitude: 2.5 mbLg
Depth: 5 km (fixed)
A small earthquake, with a magnitude of 2.5, occurred 2.5 km south of Rockford, Mercer County, Ohio, at 7:10 a.m. (Eastern Standard Time) on January 30, 2004. Although this earthquake was very small, and was clearly recorded only on Ohio Seismic Network instruments at Celina (Wright State University—Lake Campus), Lima (The Ohio State University—Lima), Springfield (Clark State Community College), and Delaware (Ohio Geological Survey/US Geological Survey), it was felt strongly throughout Mercer County, from Celina on the south to Rockford and Mendon on the north. It was most strongly felt at Rockford and Mendon, where residents described a sharp boom or thud followed by brief shaking, which rattled windows and dishes. No damage was reported. The Mercer County Sheriff’s office reported nearly 30 phone calls. Individuals who felt the event are encouraged to fill out a short form describing the effects they felt from the earthquake (USGS Community Internet Intensity Map site). This information helps to define the felt area and intensity of the earthquake.
This is the first earthquake in the Anna Seismogenic Zone since 1994 when a 2.9-magnitude earthquake occurred in Shelby County and the first earthquake in Mercer County since a 3.3-magnitude earthquake in 1977 caused a surprising degree of shaking and minor damages. The Anna Seismogenic Zone has been the site of more than 40 earthquakes since 1875, including the largest and most damaging event in Ohio’s history. This earthquake, on March 9, 1937, is estimated to have had a magnitude of 5.4 and was felt throughout a multistate area. It was centered in southern Auglaize County, but caused the most damage in the Shelby County community of Anna. Nearly every chimney in Anna was damaged and the community school was razed because of damage. The Anna Seismogenic Zone is associated with a northwest-southeast-oriented fault zone known as the Anna or Fort Wayne Rift. This zone can be traced from Champaign County, through Shelby, Auglaize, and Mercer Counties, into Indiana near Fort Wayne.
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