Geodimeter measurements from 1969 to 1975 of a geodetic network (aperture 12 km) across the San Jacinto fault near Riverside, California, indicate simple right-lateral shear accumulation at the rate 0.4 ± 0.1 μstrain/yr (engineering shear) parallel to the fault. A 12-km level line extending across the fault shows no consistent pattern of elevation change. The measured shear accumulation is interpreted in terms of a conventional dislocation model for strike slip, i.e., continuous slip on the vertical fault beneath a surficial locked zone. The observation of strain accumulation constrains the model to cases in which the ratio of the slip rate to the depth of the locked zone is about 1.2 × 10−6/yr (e.g., 25 mm/yr slip below 20 km).

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