Performance Based Seismic Design - Pick a Hazard

Earthquake hazard is a representation of the demand that will be placed upon a structure at a given site for an intensity of ground shaking. The selection of an appropriate intensity of ground shaking is a critical step in the Performance Based Seismic Design process. Earthquake hazard can be defined using probabilistic or deterministic approaches. For example, if a known fault source exists proximate to the site that has historically produced earthquakes of a characteristic magnitude, a scenario event can be defined as the earthquake hazard for consideration. For this scenario, a faulting mechanism, hypocenter, length of rupture, magnitude and duration can be selected and deterministic methods used to estimate the intensity of ground shaking at a given site.

Alternatively, a ground shaking intensity can be probabilistically selected as the shaking associated with an event that has a prescribed probability of exceedence in a prescribed period of time or an average return period. For example, building codes have historically been based on ground shaking intensities corresponding to a 10% probability of exceedence in a 50-year period of time.

The selection of an appropriate earthquake hazard permits an owner, architect or other design professional to implement a rational strategy for earthquake design that reflects the unique needs of an owner and the seismic climate of the site.