Homeowners with fire insurance are covered under the Earthquake Commission Act 1993 for damage to house and land by a natural landslip.  For house damage EQC pays the first $172,500 under s18 of the EQC Act.  For land damage EQC pays up to specified amounts under s19 of the Act for land damage plus the indemnity value of any bridges, culverts and retaining walls.  Separate house insurance policies may provide additional cover for retaining walls and the house.  The application of the EQC Act to land damage is not straightforward.  So expert advice will help.