Pulled out the 1994 California fault map (Jennings) and it looks like this swarm is pretty close to the junction of the Superstition Hills fault and Elmore Ranch fault, which failed within one day or each other in 1987 with M6.6 and 6.2 respectively. The 6.2 came first and is considered to have triggered the 6.6. (magnitudes from memory, I could be off by a tiny bit). This swarm is near the NW end of the M6.6 rupture. Anyone feel like looking into the history of swarms like this in this area (outside of the Brawley area)?. Do they tend to just swarm and stop, or are some of the larger quakes preceded by swarms?
Chris