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Description
The Elsinore fault is part of the San Andreas system of active northwest-trending right-slip faults in southern California. The fault zone extends over 200 km from the Los Angeles basin southeast to the Salton Trough. The northern Elsinore has been the site of only one well documented moderately large earthquake in historic time: the 1910 M6 Temescal Valley earthquake. This quake was located near the southern end of Temescal valley just to the south of this study. Previous slip rate estimates ranged from 0-7 mm/yr with right-lateral displacement estimates ranging from 0-40 km. Detailed mapping of late Quaternary deposits and surfaces indicates that the Glen Ivy North fault is accommodating nearly all of the dextral faulting in the Temescal Valley area. This fault has an average trend of N55°W south of Temescal Valley, N35°W within the valley, and N63°W north of the valley which results in a releasing (right) bend in the valley area. The Glen Ivy South fault, however, is accommodating primarily dip-slip and apparently results from secondary faulting due to the bend in the Glen Ivy North fault. Active southeastward tilting of the alluvial surfaces at the northwestern corner of Temescal Valley suggests that most of the deformation in this area is not controlled by normal faulting, but rather is the result of being warped downward due to extension in the central portion of the valley. Laterally offset alluvial surfaces were mapped in detail based on relative strength of the soil profiles developed within them. The soils are correlated to well dated soils in Ventura Basin to provide temporal control for the alluvial deposits. Calculation of slip rates from these data yield minimum slip rates from 3.8 to 4.3 mm/yr, maximum rates from 8.4 to 9.3 mm/yr and best fit estimates ranging from 5.3 to 5.9 mm/yr.
