Hi Dan,

The add a bit, the short response to your theoretical question is that =
there is no easy answer, it depends on what you wanted to see.  If you =
wanted to locate global events thinning your station set uniformly would =
be the best choice, but if you wanted to locate local events you =
probably would want to thin them out with a specific bias to the =
definition of "local".  It get's more complicated, if you wanted to do =
array analysis (beam forming, etc.) you'd need the station spacing to be =
appropriate for the wavelengths you were interested in observing.  There =
is no simple answer.

regards,
Chad


On Mar 16, 2011, at 9:25 AM, Brett Nordgren wrote:

> Dan,
>=20
> As the number of stations decreases and their spacing increases, the =
resolution of the process decreases proportionally.  If you want to =
record good detail you need lots of close-spaced stations.  For example, =
if there had been a less dense array, the details of the Sendai quake =
would have been more fuzzy, and less accurate.  So the plan for the =
USArray has been to have a limited geographical area for the =
Transportable Array and every so often roll it toward the East.  That =
way they can get a detailed look at what the earth is like under and =
around the US, in particular, while only requiring about 1/10 as many =
instruments.  Their Web site,    http://www.usarray.org/    tells the =
story much better than I can.
>=20
> Regards,
> Brett
>=20
> At 10:11 AM 3/16/2011, Dan Bolser wrote:
>> Cheers Brett,
>>=20
>> Indeed that visualization is incredibly cool, but I'm still not
>> getting my head round the argument.
>>=20
>> Let me try again (I'm really sorry if this is coming over as =
trolling,
>> I'm just trying to understand properly): If I were to force you at
>> gunpoint to close one of those stations (from the YouTube
>> visualization) wouldn't you be more willing to close one in the =
middle
>> of the array rather than one scattered around?
>>=20
>> If I forced you to close 50 stations, wouldn't you just thin out the
>> array in certain places rather than removing all the scattered
>> stations?
>>=20
>> Perhaps I'm getting it wrong, and you would choose to keep the array
>> intact, and selectively remove the 'outliers'. I'd be interested to
>> know.
>>=20
>>=20
>> Thanks again for the links to the very nice images.
>> Dan.
>>=20
>> P.S. I'm not proposing that we should close any stations! I'm just
>> wondering if I can use much less data to represent most of the
>> 'information'. This is a concept from bioinformatics, where you can
>> trim a protein sequence database to 10% of its original size, yet =
keep
>> 90% accuracy in terms of protein family identification of a query
>> sequence [1].
>>=20
>> [1] http://www.ncbi.nlm.nih.gov/pubmed/10871268
>=20
>=20
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>=20
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>=20
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