VOLCANO MADNESS: Re: [Geology2] Earthquake Booms, Seneca Guns, and Other Sounds

Monday, October 3, 2011

Re: [Geology2] Earthquake Booms, Seneca Guns, and Other Sounds

Excellent post, Vic! Thank you so much for sharing this info.

I must add one experience I had when I lived in SoCal and that was the night of the Hector Mine Quake. What woke me was a sound like cannon fire, but the sound seemed to come from everywhere at once.

Also, when I was a kid in rural Tennessee, we'd hear booming noises consistently. No explanation. Haven't a clue, either, as where I lived was not seismically active, at least not locally. I personally think that, considering it was the 60's, sonic booms could explain a lot of it. However, I remember hearing them like cannon fire in the distance 5 minutes apart all day long and no one was blasting in the area. Just one of those things that still intrigues me.

Lin

On Sun, Oct 2, 2011 at 8:18 PM, Victor Healey <vic.nospam@gmail.com> wrote:

http://earthquake.usgs.gov/learn/topics/booms.php

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.

Perhaps the best way to understand earthquake sounds are from an actual experiment that took place back in the 80's in California by David Hill. Dr. Hill's team recorded sounds that came out of the earth (from nearby small earthquakes between magnitude 2.0 and 3.0) and simultaneously measured the arrival of the P wave on a seismograph. Researchers also reported hearing a sound before the S waves were recorded; this turned out to be the arrival of the P wave. See this Alaska Science Forum article entitled "Earthquake Waves Outrace Sound" for a description of that experiment.