Regional phase propagation in three dimensionally heterogeneous media

The interaction of regional seismic phases with complex structure can lead to a significant modification of the seismic wavefield with the result of masking the characteristics of the source. A combination of theoretical, computational and observational studies were directed to elucidating the effect of heterogeneity on regional phases. A new method was developed for calculating the propagation of guided waves through a medium described by stochastic heterogeneity. This approach allows the estimation of the scattering contribution to the attenuation of Lg and Sn phases which can approach 30 percent for realistic heterogeneity structures. A ray based treatment was devised to describe the way in which the Lg phase is affected by changes in the shape of the crustal waveguide due to topography at the surface and the Mohorovicic discontinuity.