On August 23, as most people heard, there was a hefty but not catastrophic earthquake centered in Virginia, felt all the way up and down the eastern seaboard. Here in Vermont, many hundreds of miles north, we had the odd experience of hearing it.
Hubby and I were a couple hours into a paddling trip down a 14-mile segment of the Battenkill River between Arlington, VT, and Shushan, NY, which placed us between the southern Green Mountains / Taconic Hills and the Hudson Valley, snaking through the Battenkill's own river valley. Although the river loosely follows VT/NY Route 313, there is no regular rumbling of traffic, so things in general are very quiet, with just the chuckling water providing ambient noise. Recent rains had the river cantering along at 5+ mph, but there are no big rapids or cascades, so the sound level is essentially constant. A light westerly breeze stirred the foliage but that, too, was a low-level, susurrant background noise.
Weather was bright sun with big puffy clouds, occasionally darkening as a larger, possibly threatening cloud crossed the sun, but with low humidity and no storms forecast. Now and then between the clouds we saw high silver jet contrails but no low-flying aircraft, either private or on approach to airports or air bases (none in area), making for a dramatically fair-weather summer sky.
So, given all that, we were surprised to hear what at first sounded like a distant growling thunder; but it was prolonged and got louder, stronger, sounding at first like a commercial jet flying too low for the contrails we'd seen; but then started to sound like a military jet flying way too low on afterburners, yet not moving through space; it was stationary behind us, too low altogether to be a plane, and it stopped abruptly instead of fading off like a passing craft would. Conversely, it lacked the explosive quality of either thunder or something blowing up in the distance, or violent impact like an auto or train wreck. It lasted, I don't know, somewhere in the 10-20 seconds range, enough to get us looking over our shoulders and up in the sky and suggesting then dismissing the above explanations.
Ultimately my husband quipped, "Get ready for a tsumani!" since it reminded him of earthquakes. I felt kinda the same way. Then we forgot about it as the next section of quickwater came up and required our attention.
At the time of the noise, we were on one of the "rest" sections of the river, where the surface is still lively but you don't have to maneuver, can just float along side by side and talk or gaze around.
At end of day, when we returned to the outfitter's shop (where they provide shuttle service for paddlers), the owner greeted us at the door with "Did you hear the earthquake?" Perhaps she said, "Did you hear about the earthquake" -- unclear in the excited babble among us that followed. For all the rest of the day we looked up information about it online, talked about it with everyone, trying to understand how something so far away could have been audible.
We did not take a time note of when we heard the noise, but in reconstructing the incident realized it was near the time of the reported quake in Virginia. Could we have heard an air release through an existing fissure? An earth burp?
That's my guess. There's a phenomenon in Connecticut called the "Moodus noises" where the earth makes rumbling sounds and occasionally eerie ones in response to minor seismic activity. Since the eastern seaboard, especially the Appalachian chain, is networked with small, constantly busy movement at the micro level, it seems credible to me that we could have heard the quake as its tremors zipped all the way to Quebec.
At least, it's the only explanation that fits the nature and approximate timing of the noise.
The closest similar experience was two years ago, when a high-altitude beaver dam gave way after big rains and dumped a gazillion gallons of water down 600 feet, to carve a new canyon in the mountainside and wipe out the main road in our area. We live perhaps 2-3 miles away as the crow flies, and at the same time the deluge occurred (unbenownst to us), we suddenly heard a strange, not-quite-thunder roar out of a perfectly clear sky that lasted too many seconds. Turns out it was the sound of many tons of rock, water, and broken trees hurtling down the other side of the hill.
A bit creepy, on one hand, but fascinating and exciting, on the other.