Peak Ground Acceleration (PGA) is the maximum absolute acceleration experienced by the ground surface during an earthquake, expressed as a fraction of gravitational acceleration (g). It is the most widely used intensity measure for characterizing the severity of ground shaking at a site.
Peak Ground Acceleration (PGA) is the maximum absolute value of acceleration recorded by an accelerometer at a given location during an earthquake. It is typically expressed in units of gravitational acceleration (g) or in m/sΒ², and is one of the most fundamental parameters used to quantify the intensity of ground shaking. Because it represents the most extreme inertial demand imposed on a structure at its base, PGA is often used as a first-order indicator of seismic hazard in building codes and design spectra.
PGA is a point measurement at the ground surface β its value varies significantly with local soil conditions, distance from the rupture, and the frequency content of the seismic waves. Soft soil sites tend to amplify low-frequency motions and can produce higher PGA values than rock sites at the same distance from the source. Similarly, near-fault sites may experience directivity effects that amplify PGA in the direction of rupture propagation.
While PGA is convenient and widely used, it is not always the best predictor of structural damage. Modern earthquake engineering increasingly relies on spectral acceleration at the structure's fundamental period (Sa(Tβ)) or other intensity measures such as Arias intensity or PGV, which correlate more reliably with observed damage. Nonetheless, PGA remains the standard intensity measure for site classification, code-based design spectra, and rapid post-earthquake assessment.