According to dozens of posts on Facebook, a set of loud ground-shaking noises was heard last night in areas of eastern and northern Lebanon County, such as Avon, Myerstown, and Fredericksburg.

Although some commenters have speculated that an earthquake or tectonic shift was the cause, the USGS earthquakes dashboard shows no disturbances anywhere close to Pennsylvania. The Penn State managed Pennsylvania State Seismic Network shows a single seismic event last night, a 1.4 magnitude tremor west of Altoona.

From the reports, it’s tough to discern which correspond to the “event” and which may have been fireworks heard as part of New Year’s Eve celebration. The event itself appears to have occurred between 9:20pm and 9:30pm.

Most of the reports and discussion occurred on a Facebook post by Lebanon County Fire & Emergency Alert, which has since been deleted (this paragraph was updated at 4:30pm to reflect the deletion).

Some have speculated that the event was a meteor falling to the earth, a phenomenon sometimes called a fireball. Here is what the American Meteor Society has to say about the meteoric boom effect:

If a very bright fireball, usually greater than magnitude -8, penetrates to the stratosphere, below an altitude of about 50 km (30 miles), and explodes as a bolide, there is a chance that sonic booms may be heard on the ground below. This is more likely if the bolide occurs at an altitude angle of about 45 degrees or so for the observer, and is less likely if the bolide occurs overhead (although still possible) or near the horizon. Because sound travels quite slowly, at only about 20 km per minute, it will generally be 1.5 to 4 minutes after the visual explosion before any sonic boom can be heard. Observers who witness such spectacular events are encouraged to listen for a full 5 minutes after the fireball for potential sonic booms.

Some did report sightings of a blue flash preceding the noise, so the meteor theory seems plausible. If this were the case though, we might still expect video to emerge of the explosion moment, as captured in this 2015 video of a meteor exploding outside Pittsburgh:

No such video has been posted to social media yet of last night’s instance.

So, what else could it be?

It could have been a group setting off larger-than-normal fireworks.

It also could have been connected to the Sunoco pipeline system that runs through this part of the county. The Mariner East 2 pipeline reportedly went into service just this past Saturday, and the route does run squarely through the vicinity of last night’s event.

We have contacted Sunoco to see whether they are aware of any pipeline-related disturbances that may have occurred last night.

Do you have another theory of what happened? Video perhaps? Get in touch: Drop it in the comments or email us at [email protected].

Update 12:15pm: We have a new theory presented by Fredericksburg-based scientist Clint LeRoy, who drew on an insight he had as a HAM radio operator that radio and sound waves travel further when the air is dense and moist. With last night’s atmosphere being especially moist but mostly cloudless, it could have provided the perfect conditions for sound waves to travel far distances. LeRoy has explained this theory in greater detail in a comment below as well as a post to his Facebook profile. “This was not an earthquake. What occurred is like the ‘Perfect Storm’ with atmospheric conditions pushing the noise to greater and greater distances,” said LeRoy in the post.

While LebTown has not independently confirmed this explanation of events, it could provide a generalized explanation of how people across Pennsylvania heard fireworks and fireworks tests over unusual distances and in unusual resonance due to the atmospheric conditions.

What do you think? Remember… The truth is out there.

Update 6:15pm: The National Weather Service in State College confirmed this afternoon on Twitter that lightning strikes were observed in areas of southeastern Pennsylvania from Franklin County eastward.

The NWS confirmed that last night’s moist and dense air could have caused these sounds to travel further than they normally would.

Penn State meteorologist Steve Seman shared with us a map depicting the locations of the record strikes last night. Although the map shows strikes, none appear that close to the areas of Lebanon County where reports of the event were most widespread.

The Storm Team at WGAL 8, for one, has endorsed this explanation of events, posting this Facebook message with a recording of the station’s doppler imagery from that same period.

While this explanation certainly seems plausible, we have no actual confirmation that this was the cause of the noise. However it seems like the best available theory at this time.

It has also come to our attention that WSBT-22 in Indiana reported on a very similar sounding disturbance that occurred in that region on Sunday night. We have no reason to believe that this “loud boom” event was linked to the Monday night event in Lebanon County, but the similarity is indeed striking.

Another theory we’ve seen mentioned a few times is that someone was shooting tannerite causing it to explode. Tannerite-caused loud booms have been documented elsewhere in the country, such as a few years ago in Chautauqua County, New York and this past January in Michigan. However we have not seen any contextual evidence that supports this theory (if you have, please let us know).

Is there something else we’re missing? Have you seen any other official organizations comment on the noise? As always, you can reach us through the comments or by shooting us an email.