Petra

The general opinion is that (1) the more aftershock appear, the more stress is still left in an area. This is explicitly in Prof Keilis-Borok's predictions. There is also the idea that fewer aftershocks indicate (2) less heterogeneity in something, perhaps stress or perhaps a flatter fault or more consistant frictional properties. (1) and (2) are different ideas, and both are viable, as far as I know.

So the lack of aftershocks for the Keene event is not a red danger flag, although it is interesting that activity is showing up in so many regions after Parkfield.

However, this is an area of active research, so all these inferences should be taken with a large grain of salt.

John