 |
| Titel |
From Earth rotation to seismology - measuring rotations over 10 decades of frequencies |
| VerfasserIn |
A. Gebauer, U. Schreiber, T. Klügel |
| Konferenz |
EGU General Assembly 2012
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250065207
|
|
|
|
|
|
| Zusammenfassung |
| Ring lasers are absolute rotation sensors and allow the observation of geophysical signals
over a broad spectral range. The large ring laser “G” operating in an underground facility at
the geodetic observatory Wettzell (Germany) was constructed to monitor Earth rotation and
actually achieves a relative stability of 5 -
10-8 over an integration time of about 30 minutes.
While variations in Earth rotation occur at periods ranging from hours to days up to 1 year,
the G ring laser records signals in the seismic frequency band as well, thus covering more
than 10 decades.
In the seismic band teleseismic events, marine microseisms and locally induced rotations
caused by wind are clearly detectable. Both latter effects occur in a similar frequency range
and are denoted as noise in seismology. When combining the observed rotations with
data from collocated instruments, i.e. a three-axis seismometer and several high
resolution tiltmeters, an extensive data set of rotations, translations and horizontal
accelerations are used to study the components of the different wave fields. While the
partly coherent microseisms is present in all sensors allowing the detection of the
source direction using a combination of seismometer and ring laser data, the local
wind strongly affects the ring laser, but is weakly visible in the tiltmeter, and nearly
absent in the seismometer data. This points to a strong contribution of horizontally
polarized waves of Love type producing rotations around the sensitive axis of the ring
laser.
As the “G” ring laser yields only one component of rotation, a three axis rotational sensor is
currently developed on the basis of fiberoptic gyroscopes. This instrument is by far less
sensitive than the “G”-ring, however, it will be sensitive enough to record surface waves of
mid-size earthquakes. When combining this instrument with a seismometer or tiltmeters, the
complete deformation matrix of three translational and three rotational motions is accessible. |
|
|
|
|
|
|