Deterministic Seismic Hazard Analysis (DSHA)

Deterministic Seismic Hazard Analysis (DSHA) estimates the ground motion a site would experience from a specific, postulated earthquake scenario rather than from the full probabilistic aggregation of all possible earthquakes. The analyst identifies the seismic sources capable of affecting the site, assigns each a maximum magnitude and a closest distance, and then asks what shaking the most demanding of these scenarios would produce. Leon Reiter's 1990 text codified the four-step DSHA procedure that remains the textbook reference, situating it alongside the probabilistic framework that Cornell introduced in 1968. The output is typically a single design ground motion or response spectrum, often computed at the median or median-plus-one-standard-deviation level. DSHA answers the question 'what is the worst shaking a credible earthquake could deliver here?' rather than 'how often is a given shaking level exceeded?'. It remains central to critical-facility design, scenario emergency planning, and as a deterministic cap on probabilistic results.