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Start of funding 01.01.2006

Earthquake-Induced Rotational Motions

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In a cooperative project between the Technical University (TU) and the Ludwig-Maximilians-University (LMU) Munich an entirely new observational technology for measuring ground motions was developed in the past few years. So far, only three orthogonal components of ground motion (translations) are routinely observed in seismology, but the other three components to fully prescribe the complete motion of a point (ground rotations) have been neglected, because instruments were just not accurate enough. In a pilot project between seismology at LMU and TU geodesy a prototype “Geosensor” that measures three components of translations and the vertical component of rotation was developed and one of the prototypes was installed in 2005 at the Pinon Flat Geophysical Observatory (PFO), about 200km north-east of San Diego, CA. What does seismology expect from these new observations? We envisage in particular that (1) additional rotation measurements may help to better constrain earthquake rupture processes; (2) collocated measurements of rotations and translation allows an estimation of structural properties otherwise not accessible; (3) rotational motions are expected to also contribute to earthquake induced damage.

Final report:
This project aimed at establishing a new observable (rotational ground motions) in seismology and collecting data with the Munich-built ring laser that was installed in California (Pinon Flat Observatory near Palm Springs) in 2005. This collaboration led to the initiation of an International Working Group following a meeting in Stanford University in September 2006 and the first ever Special Issue on rotational seismology of the renowned journal “Bulletin of the Seismological Society of America” that was initiated in 2007, and co-edited by the proponent (publication in 2009). In December 2007 a special session on rotational seismology was organized for the first time at the Fall Meeting of the American Geophysical Union that is held every year in San Francisco. A joint paper emerging from this collaboration is listed below (Schreiber et al., 2009). As proposed we established a real time data connection to the Munich-steered web page of the International Working Group on Rotational Seismology (www.rotational-seismology.org). The Bacatec funded collaboration led to an invitation of the proponent as a “Cecil and Ida Green” fellow to UCSD in 2008 (sabbatical leave). As planned the funding was used to establish the operation of the ringlaser in California and for exchange visits to the partner institution. This involved a PhD student working in rotational seismology. Since the initiation of the project rotational seismology could be established as a new research field.

Reference:
Schreiber, U., J. Hautmann, A. Velikoseltsev, J. Wassermann, H. Igel, F. Otero, F. Vernon, and P.R. Wells (2009), Ring Laser Measurements of Ground Rotations for Seismology, Bull. Seis. Soc. Amer., 99, 1190-1198.