Appendix E: Effects of Natural Phenomena Hazards

DOE-STD-1020-2002

Appendix E

Effects of Natural Phenomena Hazards

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Effects of Earthquakes

For most facilities, the primary seismic hazard is earthquake ground shaking. These

criteria specifically cover the design and evaluation of buildings, equipment, distribution

systems, and other structures for earthquake ground shaking. Other earthquake effects that can

be devastating to facilities include differential ground motion induced by fault displacement,

liquefaction, and seismic-induced slope instability and ground settlement. If these latter

earthquake effects cannot be avoided in facility siting, the hazard must be eliminated by site

modification or foundation design. Existing facilities located on active fault traces, adjacent to

potentially unstable slopes, or on saturated, poorly compacted cohesionless soil or fill material

pose serious questions as to their usage for critical missions or handling hazardous materials.

While earthquake hazards of potential fault movement or other gross soil movement are

typically avoided or mitigated, the earthquake ground shaking hazard is unavoidable. When a

structure or component is subjected to earthquake shaking, its foundation or support moves with

the ground or with the structural element on which it rests. If the structure or equipment is rigid,

it follows the motion of its foundation, and the dynamic forces acting on it are nearly equal to

those associated with the base accelerations. However, if the structure is flexible, large relative

movements can be induced between the structure and its base. Earthquake ground shaking

consists of a short duration of time-varying motion that has significant energy content in the

range of natural frequencies of many structures. Thus, for flexible structures, dynamic

amplification is possible such that the motions of the structure may be significantly greater than

the ground shaking motion. In order to survive these motions, the structural elements must be

sufficiently strong, as well as sufficiently ductile, to resist the seismic-induced forces and

deformations. The effects of earthquake shaking on structures and equipment depend not only

on the earthquake motion to which they are subjected, but also on the properties of the structure

or equipment. Among the more important structural properties are the ability to absorb energy

(due to damping or inelastic behavior), the natural periods of vibration, and the strength or

The response of structures to earthquake ground shaking depends on the characteristics

of the supporting soil. The amplitude and frequency of the response of massive, stiff structures

founded or embedded in a soil media can be significantly affected by soil-structure interaction

(SSI), including spatial variation of the ground motion. For structures founded on rock media,

these effects are much less pronounced. The foundation media is, in effect, another structural

element of the structural system and changes the natural frequencies and mode shapes. That is,

the structure plus an additional foundation element may have free vibration characteristics that

differ from those of the same structure on a rigid foundation and without the additional

foundation element. A significant affect of soil-structure interaction is radiation of energy from

the structure into the ground (radiation damping). As a result, this foundation element must

represent both the stiffness and damping of the foundation media. Spatial variation of

earthquake ground motion result in reduced motion at the base of a structure from that recorded

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