Yes, it all makes sense as you say.

It is just i never saw them before
or at least never recognized them.

I have been playing around with FFT
and am taking one second chunks of data
at a time (101 samples)
to decode and below 10HZ looking at the noise
I see no contiguous signals at any particular
frequency which exceeds one second in time.

Although I can see to 50Hz My antialize filter
is at 10 HZ so that's as high as I look
between DC-0.1 and 10HZ.

It seems your imagination is the limit
in processing the data results of FFT.

Higher Sample rates give you more samples to put
into the FFT for each second of time, I think possibly the 500sps
is best if you want to look at frequencies
even below like 10Hz.

I normalize all data between zero and +/-1
before processing, don't know if this is
the right way then final results scaled
between zero and 255 for gray scale
image file display.

Don't know how many of you play with programming.
Mine is all BASIC so this C++ is a pain
to compare.

Been getting heavy low frequency micro seismic activity
in the last few hours. Possibly weather or sea related ?

Found a problem in WINSDR that is most probably the
computing power of my laptop.
I can not filter in too many different places
at the same time or it causes the recorder
to loose data and alarm causing a reset.
Works best if I only filter in one place.

Just thought Id use this opportunity to say several
things simultaneously.

Thanks for your reply.

Regards,
geoff




On 3/10/2012 9:14 PM, Dave Nelson wrote:
> Geoff,
>            not, its not the same wave doing a double trip around the world
> When the waves radiate out from the quake they go in all directions. The
> first set
> of surface waves you saw straight after your P and S waves were the ones
> that
> travelled the short path across the Pacific directly to you.
>   The second small set of waves you saw ~ 2 hrs later were the ones that
> were
> travelling out from the quake epicentre in the other direction and had a
> very much
> longer path to you and hence took much longer to arrive at your location.
> 
>  This showed up clearly on Steve's system as well as on the big USGS
> network
> where you could see the waves coming from one direction and then again
> from the
> other direction.  It was pretty cool to watch
> 
> I havent heard anyone else comment, as yet, that they also recorded the
> second
> arrival of Surface waves, but I suspect that if they looked at their
> recordings they
> may well see them
> 
> Dave
> 
> 
> At 03:20 PM 10/03/2012 +0000, you wrote:
>> I guess you have just prooven me false.
>> But in any case, i have been looking at
>> waves a very long time and never knew i saw
>> a surface wave twice around the globe before.
>> Could this EQ have been more energetic
>> than it was designated by the usgs ?
>>
>> ----- Original Message ----- From: "Dave Nelson"
>> 
>> To: 
>> Sent: Saturday, March 10, 2012 2:24 AM
>> Subject: Re: later arrival of waves
>>
>>
>>> Hi Geoff
>>>  I didnt think much of this at the time. It was only after Steve
>>> Jones's comments
>>> on his facebook page that I reconsidered your comments.  Steve
>>> clearly recorded
>>> a second arrival of Surface Waves ( not S waves) that had travelled
>>> from the
>>> epicentre and around the world in the other direction and arrived ~ 1
>>> hr after the
>>> first surface waves arrived. They passed by Steve's station before
>>> travelling further
>>> west to your location
>>> So I suspect what you saw was the same thing... those surface waves not
>>> S waves  :)
>>> cheers
>>> Dave
>>>
>>> At 10:14 AM 9/03/2012 +0000, you wrote:
>>>> I seemed to have received a second trane of S waves
>>>> two hours after receiving the P wave.
>>>>
>>>> Can this be true ?
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