What indicators would prompt upgrading a building's seismic design in a region with a newly identified hazard?

• A. New fault mapping or megathrust models, updated PSHA results, higher projected ground motions, observed ground accelerations, and revised building codes
• B. Population growth only
• C. Aesthetic renovations
• D. Doing nothing

Answer: (B)

Upgrading seismic design is driven by new information about seismic hazard, not by how many people or buildings are present. When hazard is reassessed and shows stronger or more likely ground shaking, designs must be updated to meet the new risk level. Specifically, new fault mapping or megathrust models can reveal larger fault areas or greater slip than previously thought, increasing the potential shaking. An updated probabilistic seismic hazard analysis (PSHA) can show higher probabilities of exceeding certain ground-motion levels for given return periods. If observed ground accelerations during earthquakes are stronger than what current designs assume, that confirms the need for stronger or more resilient construction. When building codes are revised to reflect these findings, it signals that existing designs should be upgraded to comply with the new standards. Population growth raises exposure and potential losses, but it does not change the hazard itself. Aesthetic renovations or doing nothing do not address the seismic risk indicated by updated hazard information.