Japan EarthQuake November 15, 2006

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Japan Earth-QuakeNovember 15, 2006

• Serendipitously recorded at MGL
• Using 5 Newly Built Pet Meters
• (The meters were not ready for shipment)

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Earth-quake recorded with seismometers in
Salt-Lake City, UT
Earth-quake recorded with PET 28 gravity meter in
Lafayette, CO
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Pre-Earthquake Data (Meters are not yet ready to
ship)
Time series data (1s) prior to earth quake. Note
that PET 35 has high drift
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After onset of Earthquake (4 hour record, 1s data)
All Plotted on Same Scale (18 mGal scale)
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Onset of earthquake from PET 28 (6 minutes)
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All Pet Meters (Time series data - 15 minutes du
ring earthquake)
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Five PET meters during earth-quake
Plotted with original feedback offsets of meters
(10 mGal)
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Cross covariance ( 5minutes Lag)
Correlation is limited to about 90-98 because
of clock differences (0.5s)
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Cross correlation ( 5minutes Lag)
Continued.
Correlation is limited to about 90-98 because
of clock differences (0.5s)
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Spectrum of 1 hour of data (after start of earth
quake)
Linear-Linear Plot
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Spectrum of 1 hour of data (after start of
earthquake)
Linear-Log Plot
Continued.
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Spectrum of 1 hour of data (after start of earth
quake)
Log-Log Plot
Continued.
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Low frequencies in earth-quake (1 hr record)
22.4 s
19.6 s
17.7 s
26.1 s
29.1 s
32.3 s
40.0 s
51.3 s
69 s
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Onset of Earth QuakeStacking of all 5 PET meters
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Onset of Earth QuakeStacking of all 5 PET
meters(a closer look at beginning)
Continued
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FFT (full)
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FFT (low frequencies)
Continued
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Plot of Frequencies in FFT
The frequencies appear to be harmonics
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Amplitude of earth-quake peaks (plotted versus
period)
(4 hours of data after start of shock)
Amplitude appears to follow power law
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Amplitude of peaks (4 hours of data after start
of shock) plotted against frequency
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Conclusions

• All five PET meters saw essentially the same
  earth-quake signal of 18mGal p-p
  
• The main differences in the signal were due to
  fact that time synchronization was not set (
  0.5s discrepancies between meters).
  
• The peaks appeared to be harmonics that roughly
  followed a power law in amplitude