Definition: Momentum = (mass) x (speed)
OK. Here we go.
Watch closely:
Divide each side
by 'mass' : <span>Momentum / mass = Speed </span>
Did you follow that ?
Answer:
Average acceleration on first part of the chunk is given as

Average acceleration on second part of the chunk is given as

Explanation:
By momentum conservation along x direction we will have

so we have


also by energy conservation






by solving above equation we will have


Average acceleration on first part of the chunk is given as


Average acceleration on second part of the chunk is given as


Kinetic energy would increase sir.
I am not sure if this is the answer you are looking for but a earthquake occurs when the plates shift.
Hope this helped.