## PSN-L Email List Message

Subject: RE: Really low stuff
From: "Stephen Hammond" shammon1@.............
Date: Wed, 30 Sep 2009 00:06:14 -0700

```I looked at you data and this is just a guess and I may be wrong and my
calculations are only estimations but... It's my understanding, the =
surface
waves continue traveling along a path around the circumference of the =
earth
in two different directions radiating out from the epicenter until all =
the
energy is dissipated. And as the timing on your plot is apx 23:00:00 UTC =
and
the event time was 17:48:00 or about 5.2 hours that would suggest that =
some
18,720 seconds had passed between the current plot and the event =
origination
time. If my guess is correct, at 4.45 KM/sec that would mean a wave =
train
traveling in one direction would have had time to travel 83,304 KM =
total.
And as the circumference of the earth is 40008 km kilometers, that would
suggest what you may have recorded was pass number two for this wave set =
as
it passed by your station. So my question is this; do you see one more =
of
these wave sets at an earlier point in the data with more amplitude?

Regards, Steve Hammond PSN Aptos, California

-----Original Message-----
From: psn-l-request@.............. [mailto:psn-l-request@............... =
On
Behalf Of Brett Nordgren
Sent: Tuesday, September 29, 2009 6:19 PM
To: psn-l@..............
Subject: Re: Really low stuff

Hi Jon,

That's what I'm hoping someone knows more about than I do.  I posted a =
gif=20
image of what we were seeing at:

http://bnordgren.org/seismo/090929.215813.bhz-ph.psn.gif

The peak amplitude appears to be about 1um/s.  Since at 180 seconds the =
50=20
sec. instrument response is down by a factor of roughly 13, the actual =
peak=20
ground velocity must have been somewhere around 13um/sec implying a peak =

Brett

At 12:44 AM 9/30/2009 +0000, you wrote:
>Hi,
>
>What was the signal that you where seeing ?
>
>Regards,
>J=F3n Fr=EDmann.
>
> > Hi all,
> >
> > As the Samoa quake was winding down, at about 23:04 UCT on the 50 =
sec
> > vertical we see a very clear ~180 second signal that lasts for about
half
> > an hour.  On the Trillium 120 Z channel it's much bigger.  What's =
going
> > on?  Is that what I think it is?
> >
> > Brett
> >

Watch our wiggles
http://bnordgren.org/seismo/gif_images.htm

or watch some very very good wiggles
http://aslwww.cr.usgs.gov/Seismic_Data/telemetry_data/ANMO_24hr.html

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