The Government announced:
Insured homeowners currently pay 5c per $100 of insurance cover, up to a maximum of $69 a year (including GST), as part of their insurance premiums. Under the proposed changes, homeowners will pay 15c per $100 of insurance cover, with an annual cap of $207 (including GST).
So if your insurance cover is $138,000 or more you pay the maximum. I doubt too many places are insured for less than that, so it is effectively a flat levy.
They reckon it will replenish the fund in 30 years. Hopefully it is at least that long until we have a major quake.