Monthly spectrograms, microseismicity 2012-01 through 2013-12

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Spectrograms from December 2013 on  |   Spectrograms for July 2009 through December 2011

A power spectrum is estimated for every hour from 1-second sampled superconducting gravity data. But first, a mean spectral background has been estimated from a succession of five days (can be/shall be improved), and the power of a particular time slice is divided by this average power. The resulting "power above mean" in dB units is indicated by colours.
   The measure of the mean here is the harmonic mean (RMS of decibel units), which emphasizes the lower values. 
   The many singular vertical stripes are caused by earthquakes. The longer-duration blobs and blotches are caused by oceanic waves, often surprisingly far away (see the live gravity monitor, MEM power spectrum); note the skidding of peak power with respect to frequency. 

2013-Jan

2012-Dec

Click for a larger image.
On Dec. 9, 2012, you may notice spectral power at a comparably high-frequency (200-500 mHz). Peek wind speed at the observatory was 20 m/s and direction easterly
2013-Feb
2012-Nov
 Between Nov. 15 and 17 you can watch microseisms to move in peek power from 200 to 130 mHz, and during Nov. 26 you can track a trace from 200 to 250 mHz. A particular short-period condition appeared on Dec 7.
   For each of these examples we will show the corresponding wave fields in the Atlantic waters. Patience please!
2013-Mar
2012-Oct
2013-Apr
2012-Sep

2013-May
2012-Aug
 Calm Sea and Prosperous Voyage - Meeresstille und glückliche Fahrt (a concert overture by Felix Mendelssohn Bartholdy, op.27, inspired by a poem by J. W. von Goethe)

Meeresstille:
  Tiefe Stille herrscht im Wasser,
  Ohne Regung ruht das Meer,
  Und bekümmert sieht der Schiffer
  Glatte Fläche ringsumher.
  Keine Luft von keiner Seite!
  Todesstille fürchterlich!
  In der ungeheuern Weite
  Reget keine Welle sich.

Glückliche Fahrt:
Die Nebel zerreißen,
Der Himmel ist helle,
Und Äolus löset
Das ängstliche Band.
Es säuseln die Winde,
Es rührt sich der Schiffer.
Geschwinde! Geschwinde!
Es teilt sich die Welle,
Es naht sich die Ferne;
Schon seh ich das Land!

2013-Jun
2012-Jul
2013-Jul
2012-Jun
2013-Aug
2012-May

2013-Sep
2012-Apr
 The white band on April 11 appears because of two major earthquakes this day, saturating the plotting range:

2012 April 11 10:43:09 UTC
    Magnitude 8.2 - OFF THE WEST COAST OF NORTHERN SUMATRA

2012 April 11 08:38:37 UTC
    Magnitude 8.6 - OFF THE WEST COAST OF NORTHERN SUMATRA
2013-Oct
2012-Mar
2013-Nov
2012-Feb
2013-Dec
2012-Jan