"This is the largest earthquake to be registered in Ohio since 1986," said ODNR earthquake expert Dr. Mike Hansen. "It follows a 2.6 magnitude earthquake registered last Friday also in the Ashtabula area."

ODNR geologists recorded the earthquake on the OhioSeis system, a 20-station network of seismographs installed by the ODNR Division of Geological Survey in 1999. The seismic network is the most comprehensive earthquake-monitoring system ever established in Ohio, and is considered by geologists to be among the best in the Midwest.

The 20 seismic monitoring stations are located at universities and government facilities in or near Ashtabula, Athens, Bowling Green, Celina, Cincinnati, Cleveland, Columbus, Lancaster, Lima, Painesville, Portsmouth, Toledo and Wooster.

The largest earthquake known to have originated within Ohio's borders occurred on March 9, 1937, in Shelby County -- measuring approximately 5.5 in magnitude on the Richter scale. In fact, Shelby and Auglaize counties, in western Ohio, form the most active seismic area in the state and have been the epicenter for more than 40 earthquakes since 1875. Ohio's other seismically active areas include northeastern and southwestern Ohio, recording 20 and 10 earthquakes respectively since the 1800s.

Ohio has experienced 120 earthquakes over the past two centuries -- enough to qualify western Ohio as the second most active earthquake zone in the eastern half of the United States, according to ODNR records.

According to Hansen, sophisticated technology used in Ohio's seismic system replaces the traditional seismograph machine, which used a pen to scribble lines across a paper drum. By using a desktop computer, Internet connection and Global Position System receiver, each unit in the new seismic network is electronically interlinked to provide quick and accurate information. The exact epicenter, magnitude and timeframe of any seismic activity can now be determined in a matter of minutes by checking data from any three or more of the seismograph units.

The 20 monitoring units in the new network are located in the most seismically active areas of the state or near regions that provide ideal conditions for detecting and locating very small tremors -- which are often undetected by humans.

The OhioSeis Network funded through the Ohio Emergency Management Agency by the Federal Emergency Management Agency (FEMA) as part of its National Earthquake Hazards Reduction Program. The computer and Internet connection at each reporting station are provided by the cooperating university or institution.

The ODNR Division of Geological Survey manages the network from its Ohio Earthquake Information Center located at Alum Creek State Park in Delaware County.

"Ohio's new seismic network provides a whole new dimension of understanding about the pulse of the Earth beneath our state," Hansen said. "Although the new seismograph network cannot predict earthquakes or alert us prior to an event, it does provide fresh insight into the risk of earthquakes in Ohio, helping us make wise land-use decisions."