Notes About Peak Ground Acceleration

One of the new observations for me during research into the behavior of some earthquakes was that the value of the horizontal acceleration of earthquakes was proportional to the value of the magnitude of the earthquake on the Richter scale in a non-direct manner.

Previously, I thought that the proportionality was linear and direct, meaning that the greater the magnitude of the earthquake on the Richter scale, the greater the value of the horizontal seismic acceleration.

But in fact, after reviewing the characteristics of more than one earthquake, it was clear that the effect of the depth of the earthquake, the center of the earthquake, is the main ruler of the value of the horizontal acceleration.

You may find that an earthquake with a magnitude of 7 Richter that occurred at a depth of 30 kilometers has a lower value for the seismic horizontal acceleration than an earthquake with a magnitude of 6 Richter that occurred at a depth of 20 kilometers.

But as for the process of estimating the seismic acceleration for designers, it seems that it is estimated on the basis of the most dangerous earthquake at the nearest point, meaning

If 4 earthquakes occur at the same epicenter, the value of the seismic horizontal acceleration will be directly proportional to the magnitude of the earthquake when the depth is constant.

Engineer Mustafa Magdy