Attenuation relationships that are used to characterize estimated ground motion often ignore details of the Earth’s highly variable 3D velocity and attenuation structure. Increasingly available attenuation models can be used to refine the expected ground motions. First, some tests are performed to look at the effect of the variability in several parameters, such as crustal attenuation, upper mantle attenuation, and crustal thickness. A concrete example is then provided using the results of a recent crust and upper mantle attenuation model of the Middle East. Variations in 1 Hz spectral accelerations of 30%–40% are found simply from the same event recorded in different directions. Because overall regional variability is expected to be even higher, this effect seems significant enough to be accounted for in strong ground-motion estimates and seismic-hazard assessment. This has the potential to account for some of the smaller scale amplitude variations not considered using broadly applied 1D attenuation relationships.

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