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Abs. High Lifetime Slip Rate Across the San Jacinto Fault Zone near Clark Lake
SCEC Annual Meeting (2010)
  • Susanne U. Janecke, Utah State University
  • D. H. Forand

We determined a right separation across the Santa Rosa segment of the Clark fault based on new mapping of a distinctive marker assemblage of biotite, hornblende-bearing tonalite, marble-bearing metasedimentary rocks, migmatite and mylonite in Coyote Mountain and the southeast Santa Rosa Mountains. We measured the uncertainty of projecting the lithologic contacts across Quaternary cover to the trace of the Clark fault and considered a range of plausible projections that conform with the structural geometry of the adjacent areas. Uncertainties are large (+3.7 km /-6.0 km) with the most likely right slip of 16.8 km. This is > 2.4 km higher than Sharp’s (1967) prior estimate which correlated the diffuse western boundary of the Eastern Peninsular mylonite zone. These slip measurements together with Sharp’s prior analysis document similar displacements across the Clark or Clark-plus-Coyote-Creek faults from Anza to the Santa Rosa Mountains of 24, 23.2, 21.9, 22.9, 25.6 and 20.3 km. There is no SEward decrease in total slip. The Coyote Creek fault displaces the same distinctive marker assemblage 3.5±1.3 km near Coyote Mountain. Field and structural analysis show that two important folds within the damage zone of the San Jacinto fault zone predate strike-slip faulting and do not record unaccounted dextral strain. The only likely locus of significant additional right separation is within the Mid Ridge fault zone roughly half way between the Clark and Coyote Creek fault. Its right slip is difficult to constrain but less than 0.5-3 km. Dividing the right separation of the Clark fault near Clark Valley by its age (1.0 to 1.1 Ma; Lutz et al., 2006) yields an average lifetime slip rate of 16.0 +4.5/‐6.2 mm/yr. Much lower slip rates since the latest Pleistocene across the central most active strand of the Clark fault zone (8.9 ± 2.0 to 1.5 ± 0.4 mm/yr; Blisniuk et al., 2010) northwest and southeast of Clark Valley, respectively, imply very large temporal changes in slip rate or far more strain in the damage zone of the fault than commonly inferred. Further analysis is needed to identify the cause of this large discrepancy. In contrast, the sum of lifetime slip rates across the two main faults of the San Jacinto fault zone near Coyote Mountain (20.1 +6.4/‐7.9 mm/yr) agrees with many GPS and InSAR-based slip estimates.

  • high fault slip,
  • san jacinto fault zone,
  • hidden slip
Publication Date
January 1, 2010
Citation Information
Janecke S.U., and Forand, D.H., 2010, High Lifetime Slip Rate Across the San Jacinto Fault Zone near Clark Lake: 2010 SCEC Annual Meeting poster 1-087.