Why are almost all Ohio earthquakes listed as occurring at a depth of 5 kilometers?
The 5-kilometer depth assigned to most Ohio earthquakes is a predetermined or fixed depth used in the location model. In most cases it is very difficult to determine the true depth to the point of initiation (hypocenter) of the earthquake unless the distance from a seismic station to the epicenter is equal to or less than the depth of the earthquake. We do know that Ohio earthquakes for which depth determinations have been made, are usually at depths of 10 kilometers or less and commonly at or near the 5 kilometer fixed depth. These depths are in the upper part of the Precambrian crystalline rocks that underlie the state.