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Andreas Wuestefeld and Goetz Bokelmann
Null detection in shear-wave splitting measurements
Bulletin of the Seismological Society of America (August 2007), 97(4):1204-1211
Abstract: Index Terms/Descriptors: GeoRef, Copyright 2007, American Geological Institute. Abstract, Copyright, Seismological Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Shear-wave splitting measurements are widely used to analyze orientations of anisotropy. We compare two different shear-wave splitting techniques, which are generally assumed to give similar results. Using a synthetic test, which covers the whole backazimuthal range, we find characteristic differences, however, in fast-axis and delay-time estimates near Null directions between the rotation correlation and the minimum energy method. We show how this difference can be used to identify Null measurements and to determine the quality of the result. This technique is then applied to teleseismic events recorded at station LVZ in northern Scandinavia, for which our method constrains the fast-axis azimuth to be 15 degrees and the delay time 1.1 sec.
algorithms; anisotropy; body waves; case studies; crust; detection; elastic waves; mantle; measurement; orientation; S-waves; seismic waves; teleseismic signals; thickness; wave splitting