Construction of Synthetics for 2D structures; core phases

Abstract

Recent studies have emphasized the prominence of anomalous high and low velocity regions in the lower mantle. For example, slower than average seismic shear wave velocities beneath the central Pacific accompanied by surrounding higher than average velocities is common to most tomographic studies (e.g., see Tanimoto, 1990; Masters et al., 1992; Su and Dziewonski, 1994). Images from these reports indicate long wavelength (> 3000 km) structures with velocity anomalies of up to ± 2.5%. A particularly prominent slow region occurs just north of the Fiji-Tonga region in all of these models and has been noted by many authors with respect to differential times of body waves, such as ScS-S by Sipkin and Jordan (1980), S-SKS by Garnero and Helmberger (1993) and others. The latter study demonstrates that S-SKS time predictions made from present 3D models do not agree with all of the observations. Since this anomaly may well be associated with up-welling currents in the mantle, the seismic details become particularly important especially at the shorter wavelengths associated with body waves (5-100 km). Thus, better methods of generating realistic synthetics for these types of complex models would be useful and are addressed in this study.