Oscillations, Waves, and Interactions - GWDG

Δf [µHz]
100
50
0
-50
Large ring laser gyroscopes 299
Kyrill@Wettzell
-100
15 16 17 18 19 20 21 22 23
Time [days in 2007]
Figure 20. Time series of G measurements taken over a week around the storm “Kyrill”
in January 2007. When Earth tides and diurnal polar motion are removed from the data, a
distinct transient feature remains in the dataset.
period of 243 days. Both the main contributors to the daily polar motion signals and
the solid Earth tides show up clearly. They agree with the literature values to within
the spectral resolution of the measurement of 50 nHz.
Apart from these known and expected signals there are also non-periodic signatures
in the time series of the ring laser, which cannot be unambiguously identified at this
point in time. Figure 20 shows such an example. The displayed dataset was taken
over 7 days around the storm “Kyrill”, which struck central Europe on the 18th of
January, 2007. One can see the diurnal polar motion and solid Earth tides signal,
which look very similar to Fig. 18. The second graph in the diagram shows the
same dataset with these known components removed. A very distinct signal remains
with a maximum on the day after the low pressure area had passed over Europe.
Neither the signal itself nor the time delay has been understood so far. For a better
illustration the actual time at which the storm passed over the gyroscope is also
marked on this plot. Apart from crustal deformation and strain effects due to wind
friction causing either tilt or some sort of local rotation also sensor internal artifacts
may be responsible for such sensor responses and the investigation of these transient
effects is still ongoing.
7 Application in seismology
With the availabilty of large ring lasers geophysical rotations became accessible at
a global scale and at various timescales [23]. In particular rotation signals from
teleseismic events became measurable for the first time [27, 29]. A specific project on
rotational seismology, funded by the German Ministry of Education and Research
(BMBF) within the geotechnology program, made the construction of a large ring
laser for seismological studies possible. Results from this project eventually led to the