What is the role of probabilistic seismic hazard assessment (PSHA) in urban planning?

• A. PSHA assigns a single deterministic ground motion value for a site.
• B. PSHA ignores uncertainty and uses only past events.
• C. PSHA provides a qualitative ranking of hazard.
• D. PSHA estimates the likelihood of different ground motion levels at a site over a time frame and informs planning.

Answer: (D)

Probabilistic seismic hazard assessment in urban planning provides a probabilistic picture of how strong ground shaking could be at a site over a chosen time horizon and uses that information to guide planning and design decisions. It combines where earthquakes might occur, how ground motion attenuates with distance, and the uncertainties in those relationships to estimate the likelihood that shaking will exceed different levels within, for example, 50 or 100 years. This lets planners and engineers translate hazard into actionable criteria—design ground motions for structures, locate critical facilities away from high-risk areas, plan zoning and retrofitting priorities, and ensure infrastructure can perform under plausible shaking scenarios.

The other options don’t fit because a single deterministic ground motion value fails to capture the natural variability of earthquakes, PSHA explicitly accounts for uncertainty and uses probabilistic, not just past-event methods, and the analysis is quantitative with probability curves rather than merely a qualitative ranking of hazard.