Hi Brett -

I recorded similar signals on both the vertical and north channel;  
however, my unit is on a cement pier which sits on dirt..........not  
very quiet.  I looked at data from 2000 - 2400, and saw other  
occurrences that had similar wave patterns.   One possibility is that  
these are surface wave packets from small aftershocks.

I found one aftershock , 21:51:01,  M 4.9, which could be the source  
of possible surface waves.   One other possibility is that these are  
wave packets of dispersive waves generated in the trailing coda of the  
main event.  I am not certain how either of these theories would hold  
up with professional seismologists, but offer them as two possibilities.

Bob Hancock


On Sep 29, 2009, at 5:17 PM, Brett Nordgren wrote:

> 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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