  In this paper, we present an analysis of seismic spectra that were calculated
from all broadband channels (BH?) made available through IRIS, NIED F-net and
Orfeus servers covering the past five years and beyond. A general
characterization of the data is given in terms of spectral histograms and
data-availability plots. We show that the spectral information can easily be
categorized in time and regions. Spectral histograms indicate that seismic
stations exist in Africa, Australia and Antarctica that measure spectra
significantly below the global low-noise models above 1 Hz. We investigate
world-wide coherence between the seismic spectra and other data sets like
proximity to cities, station elevation, earthquake frequency, and wind speeds.
Elevation of seismic stations in the US is strongly anti-correlated with
seismic noise near 0.2 Hz and again above 1.5 Hz. Urban settlements are shown
to produce excess noise above 1 Hz, but correlation curves look very different
depending on the region. It is shown that wind speeds can be strongly
correlated with seismic noise above 0.1 Hz, whereas earthquakes produce seismic
noise that shows most clearly in correlation around 80 mHz.
