Cracks in blockwork

[frediaz]

I am building a two storey house with brick and block. A few months
after completing the roof, thin cracks have appeared in an intenal
block wall and an internal block leaf on an external wall. Both on the
ground floor. But they have not appeared on the brickwork outside.

Is this something to worry about or is it because of the "natural
settlement" of the building after loading the ground floor with the
structure above, that they have told me about?

I noticed this after the earthquake in Lincolnshire. I hope it was not
because of that!

 

[^woody^]

Seems like these are aerated blocks (eg Thermalite) and if so this is a common occurrence due to too strong a mortar mix or rapid drying out.

They tend not to progress much more and can be left and plastered over if less than 5mm wide. If more then repair them.