New CPT and trench observations along the Claremont fault at Mystic Lake indicate that the main strand of the Claremont fault has jumped nearly a half kilometer westward into the San Jacinto releasing step-over during the late Quaternary. Previous seismic reflection data also suggest the presence of a young fault that cuts the middle of Mystic Lake farther west, and seismicity observations are consistent with the idea that new fault strands have formed within the step-over zone. Finally, new paleoseismic data suggest that some late Holocene earthquakes may have jumped the step-over. All of these observations suggest that the San Jacinto step-over, which has been used as the primary basis for segmenting the northern San Jacinto fault zone, is being by-passed and that the fault zone may now be capable of larger earthquakes than previously expected that may rival those on the San Andreas Fault.
