UC Santa Barbara

On 28 September 2004, the M(w)6.0 Parkfield earthquake became the most densely recorded earthquake for near-source ground-motion. To infer the kinematic nature of this event we invert the strong-motion data. The non-linear global inversion yields slip amplitude, slip rake, average rupture velocity, and rise time over the fault. By using subsets of the data, we study the dependence of the kinematic solutions on data input. The inversions reveal that the slip amplitude was less than 0.65 m and outline two major areas of slip; one that laterally surrounds the hypocenter, preferentially extending to its SE; the other 10 to 20 km NW of the hypocenter, at a depth between 2 and 8 km. The slip amplitude we obtain for each point on the fault varies less than 0.15 m depending on data set used; the rake angle variability is less than 40 degrees.