From: Nick Balaskas <nikolaos@YorkU.CA>
Date: Fri, 16 Oct 1998 12:16:44 -0700 (Pacific Daylight Time)
Fwd Date: Sun, 18 Oct 1998 14:33:11 -0400
Subject: Re: Odd Rumblings


>From: Greg St. Pierre <StrmNut@aol.com>
>Date: Wed, 14 Oct 1998 22:43:08 EDT
>To: updates@globalserve.net
>Subject: Odd Rumblings

>Dear list,

>Tonight (Wed, 14th) at approximately 7:30, I stepped out onto my
>front porch to see if the rain had stopped. As I stepped out, I
>heard what sounded like the end of a roll of thunder. It had the
>typical random changes of pitch and volume, and faded away
>quickly. This came as no surprise, as the possibility of
>occasional thunder had been forcast for today. I waited for
>another seven or eight minutes to see if I could catch a flash
>of lightning or two, but none were forthcoming. As I turned to
>go back in, two very low frequency rumbles, each of identical
>pitch and duration stopped me in my tracks. The pitch of each
>was perfectly steady, unlike the wandering pitch of a roll of
>thunder, and the two rumbles were spaced about three seconds
>apart, without overlapping.

>This was not thunder. Stormchasing happens to be a hobby of
>mine, and this was different. I once experienced a tremor here
>in NH. It happened to be very quiet at the time, and I actually
>HEARD the tremor before I felt it. This sound was closer to that
>than thunder, so my best guess would have to be a tremor,
>although I felt no ground movement. The sound appeared to
>eminate from northwest of my position in Londonderry NH, but I
>could not hazard a guess as to it's distance.

>For what it's worth.

>Greg

Hi Greg,

The place where I work has a seismometer in a vault below ground
level and a drum recorder in the main floor of one of the
buildings which I check once in a while. Although our
seismometer is very sensitive to vibrations, including some
higher frequencies that are in the audible range, it can also
pick up local "cultural" noise such as car/truck traffic on the
highway and trains moving on rail tracks many kilometers away,
not to mention noisey aircraft flying nearby and even high wind
(which causes trees and buildings to vibrate) and lake waves
beating on the shore.

If there is a seismometer within a few kilometers of where you
live (USGS, university, etc.), check it out yourself next time
you hear similar rumbling sounds. If these sounds were recorded
by three or more such seismometers, the direction and distance
of the source of the rumbling sounds can be determined.

In the quite of the night, I too have heard strange rumbling
sounds which I have attributed to the odd late airplane coming
into Pearson (Toronto) International Airport (which closes
during the night) or to long heavy frieght trains a few
kilometers away from my home. Of course, even normal noises can
sound strange in different air temperatures/densities; from
echos or and when sound reflects off nearby buildings
(interference); when the noise source is in motion (doppler
effect), etc. Maybe we should check into these strange sounds a
little bit more closely too next time we hear them.

Nick Balaskas