Back in February I checked with friends at the Delaware Geological Survey. Nothing seismic was recorded. There was no ordnance testing at Aberdeen or Wallops Island, the direction that I heard the rumble come from.
That boom was heard in Mays Landing, Vineland, Elmer, Tabernacle, and Mt. Laurel, which is a 26- by 10-mile swath running N/S or S/N. An airplane would have to pass along that trajectory to be heard in each area, yet there was no jet engine sound heard or contrails seen – at least by me. I spent a good amount of time in the outdoors but this sound was a first.
The snow peas (Oregon Giant) planted that day are now a foot tall.