Abstract

For 3–5 years following the 1989 M 7.1 Loma Prieta earthquake, creep along the southern Hayward fault, California, slowed or ceased. Slip apparently resumed pre-earthquake rates by 1994 except for a locked ∼3-km-long segment at the southern fault tip, which had consistently slipped at ∼9 mm/yr before 1989. We use repeated interferometric synthetic aperture radar (IntSAR) measurements to map active deformation along the Hayward fault while slip rates recovered between 1992 and 1995. If pure strike slip is assumed, then the slip rates estimated from IntSAR range changes between 1992 and 1995 are generally consistent with creepmeter and alignment-array measurements along much of the fault and confirm the temporary locking of the southernmost fault segment. However, along ∼6 km of the Fremont segment, IntSAR slip estimates appear to be at least twice those measured in the field. Transient vertical slip (northeast side up) of 2–3 mm/yr near the southern tip of the creep patch could explain this observation. First-order boundary-element models of a vertical frictionless fault in an elastic half-space predict some, but not all, of the inferred vertical slip.

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