17/06/2026
Earthquake Magnitude vs Intensity in Seismic Resilience.
When designing for seismic resilience, our primary engineering parameter is earthquake MAGNITUDE rather than observed INTENSITY.
MAGNITUDE represents a definitive, quantifiable physical property—it is a single, mathematically determined measure of the absolute energy released at the earthquake's source, precisely captured by seismometers. Conversely, INTENSITY is highly subjective and variable; it fluctuates based on distance from the epicenter, human perception, and the varying performance of existing, non-engineered structures.
However, INTENSITY does highlight a critical variable we account for in structural design: soil-structure interaction. While MAGNITUDE dictates the base energy source, the local soil profile dictates how that energy is transmitted. Soft soils amplify ground motion, leading to large-amplitude, low-frequency displacements (large movements), whereas stiff soils or hard rock experience shorter, high-frequency accelerations. Therefore, modern seismic codes like the NSCP 2015 take the absolute energy of a predicted MAGNITUDE, map its decay over distance, and then apply site-specific Soil Profile Coefficients to calculate the actual design forces a building must withstand.
