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Further analysis by U.S. Geological Survey seismologists has confirmed that the seismic waves recorded earlier today (corrected time: 3:42 am EST) were generated by the collapse of a mine. The longwall coal mine, is located 35 miles east northeast of Tuscaloosa, Alabama. No other damage or injuries occurred. Shaking was felt only in the immediate vicinity of the mine.
It is not unusual for collapse of subterranean structures such as mines and caves to generate seismic waves, which can be measured on equipment intended to record earthquakes (seismometers). Seismic energy can be generated by a number of events including collapse of underground structures, blasts from mining or construction, and earthquakes. Interpretation of the signals received sometimes requires detailed analysis to confirm the cause of the event. This can include the need to analyze data from a number of seismograph stations at different locations. "Data from man-made events are often very useful to seismologists because it helps us to refine mathematical models. Unlike in an earthquake, the exact location of man-made events is known and not subject to interpretation of data," according to John Unger, USGS seismologist.
