Each reactor is a separate entity although a complex with 6 reactors (e. g., Fukushima Daiichi) may be serviced with water, etc. from a central source.
Fukushima Daini complex, 7 miles distant, had design differences, including height of tsunami barriers, resistance to tremors, etc.

Somewhere above, I noted that the tsunami provision at the Daini complex was 6.51 meters but wave reached 7 meters, not causing too much damage.
At Daiichi, the severely damaged complex, the provision was 10 meters, but some estimates of the wave were more than 20 meters (from Univ. Tokyo).

The maximum ground acceleration near unit 3 of Daiichi reactor was 507 gal- or 507 centimeters /second squared- well above the plant's design value of 449 gal, according to the Japan Atomic Industrial Forum (20 March report).

Engineers use historical data to aid in design specifications, but the 9.0 quake was unprecedented. Japanese engineers are as good as any in the world; I doubt that engineers anywhere would have made provision for a quake of that magnitude at that location.

Figures released on design---- specs--- reviewed in michelekearneynuclearwire.blogspot.