The region recorded 267 shakers with magnitudes of 3.0 and above last year, compared with 125 in 2007. Seismologists said 2008 had the highest number of such quakes of any year since 1999.

What experts don't know is whether the quake cluster is a harbinger of bigger quakes to come. The 1990s was considered a seismically active decade in Southern California, producing the magnitude 7.3 Landers earthquake in 1992 and the destructive Northridge temblor in 1994. During the quake cluster of 1999, the region was hit by the magnitude 7.1 Hector Mine temblor in the desert and several sizable aftershocks. There were 828 quakes with magnitudes of 3.0 and above that year.