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Components of a probabilistic seismic hazards assessment.

Seismic Hazards at INL

In 2000, INL completed site-specific probabilistic seismic hazards assessments for all facility areas at INL. The purpose of these assessments was to estimate the levels of ground shaking that can be expected at INL facilities from all earthquake sources in the region. The seismic hazards assessments considered and incorporated results of geologic, seismologic, and geophysical investigations conducted by INL since the 1960s and published information from studies by other investigators. The probabilistic seismic hazard model included input parameters for the following:

  • Types of faulting, earthquake magnitudes, and recurrence rates (how often earthquakes occur) for fault-specific, volcanic, Snake River Plain, and Basin and Range earthquakes sources
  • Crustal attenuation models that represent the manner in which seismic waves dissipate as they travel through the subsurface in the Basin and Range and Snake River Plain crust
  • Effects to seismic waves for site-specific subsurface geologic conditions of alternating basalt and sediment layers beneath INL facilities.

Sensitivity analyses of these input parameters were performed to determine the important contributors to the seismic hazard and to assess the uncertainties in the hazard. The final probabilistic ground motion estimates are in the form of the levels of ground shaking that will not be exceeded in specified time periods such as 500; 1,000; 2,500; and 10,000 years. The longest return period (e.g., 10,000 years) has the highest acceleration or ground shaking levels and is used in seismic design criteria for nuclear reactors. The estimates were completed for surface rock conditions at all INL facilities in 1996 and updated in 2000. Additional assessments have been performed since 2000 to estimate levels of ground shaking for facilities on soil sites.

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