BGR, the Burger Joint will be selling half-price shakes at all its locations between 3-4 p.m. today. The promotion is to commemorate the earth’s shaking earlier this morning. While you can count me in the category of “I think my burps registered higher than a 3.7,” a delicious $2.50 shake is nothing I’ll shake a stick at — and a portion of the proceeds will go to the American Red Cross, so you can’t…