Shaken but Not Stirred: Rock formations reveal past quakes' size limit Sid Perkins Dozens of precariously balanced rocks in southern California tell a story just by standing there: Earthquakes that have occurred on nearby faults in recent millennia haven't exceeded magnitude 7. Researchers developing seismic-hazard maps for that and other areas are pondering how such rocky evidence might best be incorporated into their next round of updates. STILL STANDING. Analyses of this 1.3-meter-tall stone southeast of Riverside, Calif., and other precariously balanced rocks suggest that recent earthquakes on nearby faults haven't exceeded magnitude 7. J. Brune, et al. The Elsinore...