Peak particle velocity refers to the maximum speed of a particular particle as it oscillates about a point of equilibrium that is moved by a passing wave. It is a term used to describe vibration, or elastic movement, resulting from excitation by seismic energy as it passes a particular point. We usually measure this speed in “inch or inches per second.” The reason we use this measurement is that it has been shown in numerous studies over the years to be the best indicator of whether damage to a residential structure is possible or likely.