Appendix I

Starting with geological data, this paper estimates the seismicity for applications in seismic risk studies. The rate at which seismic moment is released can be estimated on a fault when the slip rate is known. Then, provided all of the deformation is released seismically, by assuming the relative frequency of different sizes of earthquakes, the absolute frequency of events can be obtained.

The frequency of occurrence of earthquakes with different seismic moments is expressed in terms of the rate of slip on a fault and to the largest seismic moment likely to occur in the region.

Historical records indicate that several meters of lateral slip along the San Andreas fault accompanied the great 1857 earthquake in central and southern California. These records, together with dendrochronological evidence, suggest that the rupture occurred along 360 to 400+ km of the fault, including several tens of kilometers of the currently creeping reach in central California.

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.

Several methods for evaluating the effect of local soil conditions on ground response during earthquakes are presently available. Most of these methods are based on the assumption that the main responses in a soil deposit are caused by the upward propagation of shear waves from the underlying rock formation.

In this paper the 100-year sample of earthquakes known to have occurred in the Puget Sound area between 1870 and 1969 ls evaluated for completeness and the question of fitting the frequency formula log N = a + bl₀ to biased samples that are short with respect to the recurrence Interval of the largest earthquakes contained 111 them ts studied.

Map

This paper introduces a method for the evaluation of the seismic risk at the site of an engineering project. The results are in terms of a ground motion parameter (such as peak acceleration) versus average return period. The method incorporates the influence of all potential sources of earthquakes and the average activity rates assigned to them.

In many cases the ground motions developed near the surface of a soil deposit during an earthquake may be attributed primarily to the upward propagation of shear waves from an underlying rock formation. If the ground surface, the rock surface, or the boundaries between different soil layers are inclined, analyses of the response of the soil deposit can be made only by techniques such as the finite-element method.