20 January 2007 -- Gravity Meters & Seismometer
Simultaneously Capture Japanese
Earthquake in Luxembourg
A Micro-g LaCoste gPhone
Gravimeter (formerly known as the Portable Earth
Tide or "PET" meter), a Superconducting Gravity Meter, and a
broadband seismometer, all
measuring simultaneously in Walferedange, Luxembourg
recorded the earthquake
centered on the Kuril Islands north of Japan on 13
January 2007.
Discussed below are:
The plots below show the response of the gPhone and the
Superconducting meter. Note that though the Superconducting
meter's output is limited to +/-7500 nm/s2
(750 microGals), the instruments stay in phase and
demonstrate remarkable agreement throughout the entire
earthquake. The gPhone data have also been integrated
to provide velocity and position information.
The following time series plots show the above response
in five minute segments, starting immediately before the earthquake.
Scroll right to see the response during the earthquake, and scroll
left to see the response during quiet seismic activity before the
quake). Note that in general the vertical scales changes from frame
to frame.
The gPhone response (velocity integrated from the
acceleration signal) is compared with that of the
Streckeisen STS-2 seismometer in the plots below. Note
that the high sensitivity of the gPhone allows it to
clearly detect the decaying Rayleigh waves which are not
visible in the STS-2 data when plotted on the same
scale.
The following time series plots again show the above
response, but in five minute segments. Again, the
plots start immediately before the earthquake. Scroll
right to see the response during the earthquake, and
scroll left to see the response during quiet seismic
activity before the quake). Note that in general the
vertical scales changes from frame to frame.
For a more detailed look at the results and correlations
between the instruments, please click here. Also,
for a related discussion of five gPhone Gravimeters measuring a
November 2006 earthquake, please click here. These data are
courtesy of Olivier Francis, Faculte des Sciences, de la
Technologie et de la Communication, University of
Luxembourg.
- Distance from Japan to Luxembourg, forward arc:
8944km
- Distance from Japan to Luxembourg, reverse arc:
31087km
- Modeled Rayleigh wave velocities: 3.97km/s
forward arc, 3.54km/s
reverse arc (higher velocity across Eurasian craton)
- Model travel times (forward, in hours): 0.70,
3.83, 6.96, 10.10
- Model travel times (reverse, in hours): 2.43,
5.56, 8.70, 11.83
Plotted above is the gPhone response to the earthquake
integrated twice to get the vertical displacement. Note the
clear onset of the Rayleigh waves at approximately 0.7 hours.
In
this plot, the green marks indicate the Rayleigh wave
arrival times as observed by the gPhone, and the red
marks indicate the model-predicted times.
Here the waves are plotted on a vertical log scale.
Note the exponential fall off of the power.
Please click here for a pdf
file of these Rayleigh response figures.
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