SAN DIEGO – Residents reported feeling rattling and hearing a "boom" Thursday morning.
People reached out to FOX 5 around 11 a.m. after experiencing the shaking.
"We felt an earthquake in Rancho San Diego a few minutes ago! Lots of people did!" one person said.
In Skyline, a woman heard the boom just before 11 a.m.
"[I heard it] about 15 minutes ago. Not sure of the direction. But my house shook and my curtains blew inward."
"I heard the boom ! I live in Spring Valley thought it was construction, but I didn't feel any shaking," another person said. "About a week or two ago I heard the exact same boom and few seconds later my bed and walls started rocking it stopped for like 2 seconds and started shaking again. I didn't see any reports on an earthquake that day and I asked people if they had felt it and no one did so I just ignored it."
Fox 5 made dozens of calls to find out what it was.
USGS did not report any earthquakes in the area around that time.
A training session at Camp Pendleton was scheduled for Thursday, although military officials said the impact from live mortar fire would not be felt or heard to the degree it was reported.
A local rock quarry told Fox 5, a blast was conducted, but it was yesterday.
U.S. Navy officials said jets launched off the U.S.S. Carl Vinson, but it wasn't until after 11 a.m.
Geologist and Weather Expert Dr. Pat Abbott told Fox 5 it's likely the answer lies above us.
"If anything happened in the ground we would have known, because we monitor that. So, that means it’s up in the atmosphere," said Dr. Abbott.
He said it's likely the sound actually came from far away.
"It might have been a quarry blast in another county, for example something like that that got reflected towards us," said Abbott.
He said San Diego has been experiencing changing weather, which creates layers in the atmosphere.
"You can get enough contrast between colder air and warmer air for example that will almost act like a reflecting board," said Abbott. "So some sound can go up hit some other surface and go over an area like an unexpected area."
Abbott said it is a theory actually dates back to the days of the Civil War.
"They had observers watching the battle and they would have guns being shot, but you wouldn’t hear much of anything. Meanwhile a village on the other side over the hill, they were being overwhelmed with noise. Why? The atmosphere reflected the sound and went the other direction," said Abbott.
San Diego police and sheriff's departments were also investigating, but they also did not have a cause.
Did you feel or hear it? Tell us what you experienced on our Facebook post.