why us the type of rock/crust present in an area considered a major factor for the damages caused by an earthquake​

Explained below

Explanation:

The magnitude of an earthquake may likely vary with how soft the crust/sediments of the area are.

Now, the seismic waves of an earthquake usually when travelling through the ground move much faster through hard Rock than through soft soil.

Now, when these waves make a transition from the hard to the soft earth, this leads to a bigger amplitude and thus leads to a stronger earthquake shaking.