I started this thread as "heartland chris". That was a mistake; I am now Island Chris.
The larger quakes tend to have shifted slightly to the northwest with time, suggesting that these are on a San Andreas-parallel fault if not the San Andreas proper. That's assuming that the precision of the locations is within a couple hundred meters.

most of the bigger ones are 6 to 8 km depth. A couple are much deeper but those locations may not be accurate. The crust is very hot in Brawley so it is possible that a large quake will not initiate as deep as most other places in California.

Chris