Project

The Geosensor stands for the concept of collocated measurements of translations (using a standard seismometer) and one to three components of rotations using for example ring laser technology. The principle of ring laser technology is described on the www pages of the Fundamentalstation Wettzell.

Since the G-Ring at Wettzell has been operational dozens of seismic events have been recorded and are now being processed (e.g., Igel et al. 2005a). At present the focus is on analysing teleseismic events. Due to the near-plane phases that are observed rotations can be compared to transverse accelerations as they are in phase under certain conditions. It could be shown that the observations are consistent with broadband recordings of translations. We argue therefore that rotation is a new consistent observable that may be useful in several areas such as earthquake physics, shaking hazard, earthquake engineering, seismic tomography and geodesy. We plan to make permanent data and event data as well as processing results available here soon.

As rotations are related to the curl operator of the seismic wavefield they can be derived from seismic arrays. In order to compare array-derived rotations with direct measurements of rotations with the G-ring at Wettzell we installed a 9-station array in December 2003 for a duration of 4 months. This provided the first ever data set where array-derived rotations can be compared with direct measurements and the results are very interesting and will be published shortly (Suryanto et. al, 2004, 2005). Further information on this experiment can be found here.

There are very few studies on rotational motions in seismology even though theoreticians (e.g. Aki and Richards, Quantitative seismology, 1980, 2002) have argued for decades that rotations should be measured. It is at present unclear, how structural heterogeneities, complex seismic sources, anisotropy and various rheologies affect rotational motions. These topics are currently investigated using analytical and numerical tools.