When I lived down there, we'd get loud booms and a good shake every now and then. It was usually attributed to the the Marines at Camp Pendleton "not" doing maneuvers, uh huh.
My wife said lamp shades were swinging at my house... near SlashX Café. I was up in Big Bear. We think we know what caused it:
Went to the inlaws to get a patio cover back in the air. It's way fun cruising the tall lumber isle at Home Depot when a 4.1 aftershock hits.