Hello everybody -
I've joined this group on the suggestion of a friend who records
nature sounds for musical composition. I am a grad student who is
looking into recording wave signatures from (and hopefully preceding)
landslide events, in particular, rockfalls in Yosemite National Park.
Previously, I have installed seismic instrumentation. There is much
to be learned from seismic studies - one obvious objective is whether
or not the rock makes "noise" prior to failure. My guess is that yes,
in fact, it does, but you'd have to have seismic instruments quite
close to detect this fracturing (for example, they do this in
underground mines, but the instruments are recording seismic waves in
the audible range, and they are within 10 meters). Hence, it may not
ever work from a practical standpoint.
I'm starting to think that, for prediction of failure at least,
acoustic recordings would work quite well. There have been scattered
reports of audible "cracking" noises in the hours preceding a
rockfall. Those who reported it were in the bottom of the valley,
could not identify where the sound was originating, and didn't think
until later that those sounds might be associated with rockfall. I've
never heard them myself. Furthermore, the recent rockfalls at Curry
Village (link to a news article here ->
http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2008/10/08/BAHH13DJRN.DTL
) crushed cabins that, just minutes prior, housed schoolchildren, very
scary. Hence, now is the time to ask for and install experimental
monitoring systems.
Now, I have no experience in this whatsoever, am looking for
suggestions on microphone systems (and possible entire recording
systems) capable of withstanding bad weather, probably directional,
and recording continuously for, at least, a few days (then
overwriting?). Budget is unknown, but prob'y on the small side
($couple thousand??). Microphones will be located about a mile from
the site of the cracking (think sitting in the valley, pointing up at
a remote cliff face, but with nothing in the way). Perhaps up to 20
kHz (the cracking has been described as popping, perhaps like gunshots)?
I have more ideas about sending the recorded signal into a database
used by seismologists running "triggering" logs, which would then
prompt the system to download the entire waveform and send over the
internet to be reviewed (this assumes that the microphone is located
on a building, attached to a computer inside), etc, etc etc.
Thanks for reading... I'll go and do some homework on this on my own,
and ask more questions later -
- Valerie Zimmer
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