I have the same problem with my house in the boston, ma us area,have had the cracks filled with epoxy, have had the foundation stucco redone, cracks again and again, finally had an engineer look at it a couple of years ago, and they stated from his report that it was expansion and contraction of the ground during seasonal changes, we have a 100 degree tempeture swing here in the north east us,so you should have an engineer look into it it cost me $1,000 and at least I know what is happenning officially, the engineer said short of replacing the foundation there was no way to stop this, I just had the corner that was the worst cracks to date re-epoxied and they mud jacked the slab under the house corner which was built directly on top of blue stone ledge, so far it has been 2 years and no more cracks. Good Luck!