8.6 Factors Affecting Ground Motion:

Factors that affect strong ground motion include:

(a) Wave types—S and P waves that travel through the earth, as well as the surface waves that propagate along the surfaces or interfaces.

(b) Earthquake magnitude—There are several magnitude scales. Even a small magnitude event may produce large accelerations in the near field. Consequently, a wide variety of acceleration for the same magnitude may be expected.

(c) Distance from epicenter or from center of energy release.

(d) Site conditions.

(e) Fault type, depth, and the recurrence interval.


The selection of a design earthquake may be based on:

(a) Known design-level and maximum credible earthquake magnitudes. These are associated with a fault whose seismicity has been estimated.

(b) Specification of probability of occurrence of the earthquake for a given life of the structure (such as having a 10 percent chance of being exceeded in 50 years).

(c) Specification of a required level of ground motion. This specification is available in the code provision.

(d) Fault length empirical relationships.