What are Ground Motion Prediction Equations (GMPEs) used for in hazard analysis?

• A. They describe the tectonic plate movement.
• B. They are empirical relationships that predict expected ground motion as a function of magnitude, distance, and site conditions.
• C. They provide budgets for hazard mitigation.
• D. They forecast tsunamis directly.

Answer: (B)

GMPEs are empirical relationships that link the expected ground shaking at a site to the characteristics of the earthquake and the local environment. In hazard analysis, they’re used to estimate how strong the ground motion might be for a given earthquake scenario by relating magnitude, distance from the source, and site conditions (like soil type or Vs30) to measures such as peak ground acceleration or spectral acceleration at different periods. These equations come from many recorded earthquakes and include variability to reflect natural differences in shaking.

This makes GMPEs central for probabilistic seismic hazard analysis, where we combine the likelihood of various earthquakes with their predicted ground motions to build hazard curves and design spectra. They’re not about describing tectonic plate movement, providing budgets for mitigation, or forecasting tsunamis. Their purpose is specifically to predict ground motion levels based on magnitude, distance, and site effects so engineers and planners can assess and design for expected shaking.