Unlike the famous San Andreas Fault, nearly all of Indiana's faults are buried and cannot be seen at the surface. Nevertheless, researchers have been able to map some faults using information from oil and gas wells and by employing geophysical methods. Most of the mapped faults are in the southwestern corner of the state. These faults extend into southeastern Illinois and western Kentucky and are collectively known as the Wabash Valley Fault System.
Most of the mapped faults are within one kilometer of the earth's surface and are unlikely to be the cause of earthquakes. The earthquakes that have occurred during the last 200 years are the result of movement along faults at much greater depths (10 or more kilometers). Because such earthquake-generating faults are so deep, geoscientists have difficulty mapping them. More research is needed before we will know the full extent of faulting at great depth and the potential for movement along those faults.
Additional information on Indiana’s seismicity is available from the United States Geological Survey.