How does the USGS tell the difference between an earthquake and a sonic boom?

Steps to identification of a sonic boom:

• The USGS sees either nothing on our seismic records or a fairly short high-frequency signal that doesn't look like an earthquake.
• On rare occasions, we see the event on multiple stations, and the time difference between stations matches the speed of sound in air, which is slower than the speed of seismic waves in rock.
• Felt reports come from a wide area, which is typical of a fairly large earthquake, but no such event is on our records. 
• Reports of a bang are a clue that it's a sonic boom, but not an ironclad indicator since shallow earthquakes often sound like booms or bangs.
• All of the above indicates an atmospheric source such as a sonic boom, artillery fire, or a meteorite or bolide explosion. Bolides are often accompanied by bright light, sound, and ground motion.
• The final step is getting the military to admit responsibility. In most cases, the best we get is a confirmation that there were planes in the area that "might have gone supersonic."