September 30, 2011 – CHARLESTON, SC – A loud boom shook the coastal Lowcountry Wednesday morning, felt from Mount Pleasant to West Ashley. And once again, no one could say what caused it.
Seismographs at the College of Charleston didn’t pick up any earthquake activity. The Charleston Air Force Base didn’t report any military aircraft creating sonic booms. No commercial vessels responded to a U.S. Coast Guard message asking for reports if it had been felt offshore.
The reverberation most likely came from the “Seneca Guns,” a so-far-unexplained phenomenon felt along coasts around the world.
Some experts speculate that the booms are caused by gases released from the sea floor, or undersea landslides along the Continental Shelf, or the echoed sound of distant thunder, or lightning-like electrical discharges, or even meteors crashing into the atmosphere at angles.
The latest blast hit just before 10 a.m. “It was a pretty good shake, a pretty loud boom,” said Mark Reamer, who felt it in the Financial Management. “The mirrors on the wall rattled,” said Melinda Issacson, who was working out at home on James Island. Doors, windows and houses shook in Mount Pleasant and on Sullivan’s Island, according to Twitter reports.
A West Ashley tweeter said it sounded like a gust of wind against the house. About the same time, a large tree fell across Hut Road on Johns Island and a nearby resident reported an explosion. But a tweeter in North Charleston said nothing was felt there.
Small quakes and other booms are regular occurrences in the Lowcountry, where a series of faults converge underground. The last big shake was a temblor from the 5.8 Richter scale quake in Virginia in August. In March, a succession of three loud booms shook the coast that were widely believed to be the Seneca Guns. –Post and Courier
Earthquake Booms, Seneca Guns, and Other Sounds
Introduction & Basics
Earthquake "booms" have been reported for a long time, and they tend to occur more in the Northeastern US and along the East Coast. Of course, most "booms" that people hear or experience are actually some type of cultural noise, such as some type of explosion, a large vehicle going by, or sometimes a sonic boom, but there have been many reports of "booms" that cannot be explained by man-made sources. No one knows for sure, but scientists speculate that these "booms" are probably small shallow earthquakes that are too small to be recorded, but large enough to be felt by people nearby.
As it turns out....there are many factors that contribute to the "sound' that an earthquake makes. To begin to understand these factors we have to understand the different types of waves, the speed they travel through the earth, and the speed that sound travels through the air.
'Pretty good shake' hits area, but what was it?
By Bo Petersen
Thursday, September 29, 2011
Here is a site you can use to find reported "fire balls" in your area...http://www.amsmeteors.org/fireball2/public.php?start_date=2011-01-01&end_date=2011-12-31