HR: 0800h
AN: S31B-1058    [Abstracts]
TI: Comparison of ring laser rotational measurements with rotations derived from seismic array data: the M6.4 Morocco earthquake of February 24, 2004
AU: * Suryanto, W
EM: wiwit@geophysik.uni-muenchen.de
AF: Department of Earth and Environmental Sciences, Ludwig Maximillian Universit�t Muenchen, Theresienstr 41, Munich, 80333 Germany
AU: Vollmer, D
EM: daniel@geo.uni-potsdam.de
AF: Institute f�r Geowissenschaften, Universit�t Potsdam, Postfach 601553, Potsdam, 14415 Germany
AU: Wassermann, J
EM: jowa@geophysik.uni-muenchen.de
AF: Department of Earth and Environmental Sciences, Ludwig Maximillian Universit�t Muenchen, Theresienstr 41, Munich, 80333 Germany
AU: Igel, H
EM: igel@geophysik.uni-muenchen.de
AF: Department of Earth and Environmental Sciences, Ludwig Maximillian Universit�t Muenchen, Theresienstr 41, Munich, 80333 Germany
AU: Scherbaum, F
EM: fd@geo.uni-potsdam.de
AF: Institute f�r Geowissenschaften, Universit�t Potsdam, Postfach 601553, Potsdam, 14415 Germany
AB: Recently, ring laser technology has provided the first consistent observations of rotational motions induced by distant large earthquakes. Consistent in this context implies that the observed waveforms and amplitudes are in large part compatible with the theoretical prediction that - assuming plane wave propagation - transverse acceleration and rotation rate should be in phase and their ratio identical to twice the horizontal phase velocity. The ring laser installed at the Fundamentalstation Wettzell, South East of Germany, is recording the vertical component of rotation rate. Theoretically, this vertical component of rotation rate is a linear combination of the space derivatives of the horizontal components of translations. This suggests that - at least in principle - rotation could be determined from seismic array measurements using "finite differencing". For this purpose, we installed a cross-shaped array of nine (LE3D/5s-Mars Lite) seismometers around the ring laser instrument in Wettzell. The experiment was running for four months, from December 2003 to March 2004, recording several large earthquakes. The data set is complemented by the GRSN broadband instrument installed at Wettzell. Space derivatives are calculated by applying three different methods: A derivative weighted constant based on polynomial inversion, derivative calculation using triangular points and geodetic inversion of the surface strain and stress tensor as function of time from observed displacements. These procedures were applied to the M6.4 Morocco earthquake of February 24, 2004. We note that this is the first experiment where - in addition to seismic array data - direct measurements of a collocated rotational sensor are available.
DE: 7212 Earthquake ground motions and engineering
SC: Seismology [S]
MN: 2004 AGU Fall Meeting