We analyze, both physically and numerically, certain effects of shear-wave propagation in orthorhombic Phenolic CE (PCE). This industrial laminate provides a physical model for the study of wave propagation in orthorhombic media and has been used in several laboratory experiments. Recently, we observed polarity reversals on seismogram traces along two profiles through a sphere of PCE. The observations were attributed to the rapid variation of polarization in the neighborhood of slowness-surface conical points (point singularities). We now present results of numerical modeling experiments that show amplitude variations similar to those observed in the physical modeling. For receiver positions along a symmetry plane of the anisotropic medium, these amplitude variations may indeed be attributed to rapid polarization changes due to conical points. For a profile crossing a symmetry plane, however, the numerical examples indicate that relatively smooth variations of the displacement can result in rapid amplitude variations (polarity reversals) on seismogram traces, depending on the particular source-receiver configuration used. The computed seismograms also show characteristic Hilbert-transform-type waveforms due to wavefront folding. This folding is a direct result of slowness-surface conical points and the related waveform characteristics may be used in future experiments to detect conical-point effects. The detectability of these waveform variations depends strongly on the frequency range emitted by the source, i.e., the transmitting transducer.
AGU Index Terms: 7203 Body wave propagation; Mineralogy, Petrology, and Rock Chemistry; 7260 Theory and modeling; 7299 General or miscellaneous; 7200 SEISMOLOGY
Keywords/Free Terms: Anisotropy, numerical modeling, physical
JGR-Solid Earth 96JB02117
Vol. 101
, No. B12
, p. 27,765