Barbara,

What you're seeing now is a return to normal. As John V so aptly pointed out the stress shadow from the 1906 quake is lifting and as it does so we will see more activity and certainly more 3's and later more of everything else.

Personally I think it is more related to Loma Prieta because that's when the perverbial faucet was shut tight. But no matter, one thing is for sure, a 4.0 quake there equals damage to windows and chimneys falling as the quakes are so shallow.

I suspect Piedmont will be the place to see the first 4.0 as it has had more activity lately. But I could be wrong, sometimes I am and sometimes I'm not; but I'm always curious.

Petra