Earthquake Sounds. Shake, rattle and roll

Pano

Administrator
Paid Member
2004-10-07 6:05 am
Panama
The 1st day of spring started with a bang here on the Big Island of Hawaii. We had a cute little 4.6 magnitude earthquake just after dawn. Rattled the windows and made a nice Bang!

What really intrigues me is that so many earthquakes like this start with a low rumble, a rumble that makes me think "Big Truck", then the shaking starts. What is that rumble? I mean what frequency? It's low, but not super low.

I've obtained some seismographic data from the nearest monitoring station on Mauna Kea. It' in 2 column ASCII format, with date and time in the left column, magnitude in the right column. I want to work on the data a little to see if I can convert it to audio, or other data for spectrum analysis. Anyone done this before? How did you do it? I'm thinking that some of my wave editors could import it, if it's in the right format.
 

Pano

Administrator
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2004-10-07 6:05 am
Panama
I got data form the USGS. It's sampled at 30Hz, which is really too low for my needs, but I'm giving it a try anyway.

No falling out of bed, Cal. Just a mild one, nice shake. You must get those too.

Yep, I'll try to contact some local seismologists to find out if they already have what I need. They probably do. But I did kinda want to Do It Yourself :)
 

Pano

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Paid Member
2004-10-07 6:05 am
Panama
My problem seem to be importing the data. I can actually export audio files as text with Audacity, but it has no function to import them. Importing as RAW does not work, as that expects a binary file.
Might need a MATLAB script to convert from the text to RAW.
 

Pano

Administrator
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2004-10-07 6:05 am
Panama
Bigger than you think. The main office is 100 miles from here (160km). But pie is always welcome.
I did find some earthquake sound files on the USGS site. Not Hawaii, but it's something.

Seems most of the rumble is around 40-50Hz. Or like an open E or open A string on a bass.
Of course there is plenty of infrasonic energy, but the main audible parts of the files I got was in the bass E,F,G,A range. Rumble, without many audible harmonics.
 

Pano

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2004-10-07 6:05 am
Panama
Here are some plots pulled from 3 quakes on the USGS website. The 3rd is lower than the other two, don't know if that 20Hz would be audible or not. I hope to get some files from today's shaker.
 

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Bigger than you think.
Yes Michael, I was having a spot of fun with you.
But pie is always welcome.
Show me a man who doesn't like pie and I'll show you a hairdresser.
Of course there is plenty of infrasonic energy, but the main audible parts of the files I got was in the bass E,F,G,A range. Rumble, without many audible harmonics.
Now you're just confusing me, stop it.
 

Zero D

Member
2009-08-06 11:11 am
@ Pano

I've only experienced 1 earthquake here in the UK about 5 years ago. It woke me up & felt Very wierd. Not a 4.6 though !

I didn't know you could export an audio file to .txt with Audacity ? I just tried it and saw no option to do that ?

Anyway i experimented on my desktop by changing the extension of a .WAV file to .txt I was able to drag/drop that into Audacity perfectly. I know there's a difference in what you want to convert, but thought you might like a heads up to experiment in various ways to try & get it to work.
 
I got data form the USGS. It's sampled at 30Hz, which is really too low for my needs, but I'm giving it a try anyway.
Seems most of the rumble is around 40-50Hz. Or like an open E or open A string on a bass.

"one of these things is not like the other..."

How does one represent 40 to 50 hz signals using a 30 hz sampling rate?

John
 

Pano

Administrator
Paid Member
2004-10-07 6:05 am
Panama
How does one represent 40 to 50 hz signals using a 30 hz sampling rate?

I did find some earthquake sound files on the USGS site. Not Hawaii, but it's something.
Completely different data and file formats. I should have explained it better, sorry. The files I analyzed are in .wav format with a 8k sample rate. They are from some quakes on the mainland. The files I got from the local monitoring station are in a text table form, time and amplitude, 30 times per second. Good to see the shakes, not good to analyze sound.