Hi,

This might be traffic (car, trains, people) or wind noise. This noise is
common from 3Hz and upwards. If you see period change in the noise
during the day and weekend, it is traffic noise from cars nearby. But
this type of sensors can pick up car noise from up to 5 km away if the
ground allows for it (mud, clay type of soil).

Best regards,
J=C3=B3n Fr=C3=ADmann.

On m=C3=A1n, 2012-07-30 at 02:07 +0000, Tiago A. wrote:
> Hi.
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> Im using a L4 1Hz geophone and for almost a month im struggling with
> high noise from 10s up to ..., but from <10s it looks good. The noise
> comes and goes, this image is self explaining:
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> http://dl.dropbox.com/u/15802004/noise.png
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> Changed cables, re centered the geophone, but didint help..the
> geophone is connected directly to a ADC without damping, external
> amplification or filtering, i only use digital filtering from the ADC.
> Before this issue start, i had a pretty clean spectrum >10s for almost
> 6 months, which allowed me to received LQ and LR from some strong
> events.
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> This sac contains 15minutes with high noise >10s, notice that at 3:37
> it recorded a Ml2.1 at 70km.
> http://dl.dropbox.com/u/15802004/noise.sac
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> What could be the problem?=20
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> I appreciate any help.
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> Best Regards,
> Tiago.
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