Petra,

We're not sure.

Some think that more aftershocks mean there is more stress left in the region after the mainshock, hence more mainshocks might be more likely. This trend would make the Santa Barbara quake less ominous.

Other guess that more aftershocks means that there is more heterogeneity of something; stress, structure, frictional properties, which is not easily translated to risk.

The red flag for some prognosticators is an accelerating rate of foreshocks, of course we don't know that they're really foreshocks until the mainshock hits.

Some trends that have been observed: Deeper quakes have fewer aftershocks (this quake at 16 km is fairly deep, if the depth is right, which can be hard to estimate offshore).

Some consider foreshocks and aftershocks a sign that fluids are gushing around in the hypocentral region, for whatever that is worth.

John