Walter J. Silva

A formulation extending the Haskell-Thompson matrix method to include the effects of anelastic attenuation is presented. The formulation is exact in that no low-loss approximations are made. Consideration is given to nonparallel propagation and attenuation directions with corresponding velocity anisotropy. Examples are presented for models representing soils, the crust, and the core-mantle boundary.

Recommendations for seismic design ground motions for nuclear facilities require a consistency with both observed strong motion data and with seismological theory on the characteristics of strong shaking. Different recommendations are appropriate for various regions of the US, because both earthquake source characteristics differ and the earth's crustal properties vary with region.

In previous ground-motion models, the range of applicability of the empirical ground-motion models was based on the range covered by the available empirical data set; however, in hazard studies, the ground motion must be computed for all relevant earthquakes, so the limits on the range of applicability were often ignored. To address this issue, the Next Generation Attenuation (NGA) project required the developers of the models to extrapolate their models such that they are applicable to all crustal earthquakes relevant for seismic hazard analyses in California.