Tectonics question on why Earthquake damage varies!!

Geology is one factor affecting the damage caused by earthquakes.

The book says that areas with hard rocks experience less damage from earthquakes than with softer rocks like sands and clays.
I understand that with soft rocks you get more damage due to liquefaction and sinking buildings etc.

But surely, seismic waves (P and S) do more damage when they travel slowly through solids? And they do less damage when they travel quickly - which would be through soft rocks as there's less resistance?

So surely that's contradicting the statement above?

I don't get how Hard rocks mean less damage is done

Also, sorry if this doesn't make sense :'

Hi MapleMaypole!

I think you've confused yourself a bit with how the velocity of seismic waves changes through different rock types. Seismic waves travel more quickly through solid, hard rocks such as granite, because they are able to pass through the rock easily. On the other hand, seismic waves travel more slowly through softer, weaker rocks such as clay, because some of the seismic energy gets absorbed and the waves can't pass through as easily

Thank you for that explanation!!
That's very helpful!!!!!!

You're welcome, I'm glad I could help

Hello!
I just read in my notes that harder rocks absorb more energy? Which sort of makes sense too as if they absorb the energy then there's less impact on the people/property.
Does this relate to speed of waves through rock or not?

Correct me if I'm wrong!!

Hi Maple!

My understanding is the opposite: hard rocks absorb less seismic energy because they allow the seismic waves to pass through quickly (due to the particles within the rock being unable to move/only move a small amount), whereas soft rocks absorb more seismic energy because the particles are able to move more freely, slowing down the progress of the seismic waves

That makes sense too! Especially as you mention the speed of the waves. It makes sense that softer rocks will absorb more energy, slow down the wave and cause more damage.

But it also makes sense that hard rocks absorb the energy and reduce the impact. It just doesn't explain wave speed.

I'll have to ask my teacher after the Christmas hols which one is correct!

Okay! I shall have a go at answering your predicting earthquakes question too btw, I have seen it

Okay! I shall have a go at answering your predicting earthquakes question too btw, I have seen it

My Geography teacher said that hard rocks absorb more energy from the waves and therefore less damage occurs

Hmm, that's odd

I'll tag in @Plagioclase to see what he thinks of this