What is the near-field?

Except in the presence of unusual geotechnical effects or highly vulnerable buildings, extensive damage to structures is generally limited to an area close to the source of energy release in strong earthquakes. Accelerograms obtained in recent years close to the source of strong earthquakes reveal exceptional features that challenge some widely held concepts about the nature of strong motion. The area close to the earthquake source is commonly referred to as the "near-field" but there is no consensus as to what this means. Some definitions of near-field are reviewed and compared. A general framework to define near-field is presented considering both strong-motion and structural response parameters. This approach is shown to effectively constrain a magnitude-distance space to be near-field from an engineering viewpoint.