Peak Ground Acceleration PGA, PGV, PGD

Peak ground acceleration (PGA) is the maximum acceleration of the ground by earthquake. However, the acceleration in the structure is higher because of dynamic amplification. In fact, for an average building the acceleration could be increased up to 2.5 to 3.0 PGA (Melbourne). Rigid buildings are controlled by acceleration. PGA can be well measured using strong motion accelerometers placed close of the epicenter of the earthquake. The response of the structure depends on the duration of the pulse and the time history as a whole, and not just the PGA.

Peak ground velocity (PGV) gives more information about the response of structures, being a better indicator of damage than PGA. The difference between PGV and the velocity in the center mass of structure is less than PGA and a, that is to say, the velocity (V) is 1.8 to 2.0 PGV. Buildings less rigid are controlled for velocity. PGV can be measured by seismometers place far away of the epicenter, which could be quite complex. PGV is also related to MMI intensity and with the PGA = PGV/750 (All the values for Rock in Melbourne)

Peak ground displacement (PGD) is related to the drift of the building. In this case, the displacement of the center mass is 1.4 to 1.5 PGD. However, it is not possible to measure directly, but could it be calculated using advanced seismometers, like tele-seismometers from a long distance. Flexible buildings are controlled by displacement.

Finally, the duration of a shaking depends of the fault size and duration of the rupture. Nonetheless, the duration can be prolonged by features in the wave transmission a geological site. For instance, soil could amplify the seism and increasing the dynamic properties of the earthquake, such as this happened in the Mexican Earthquake of 1985.