Alquist-Priolo Earthquake Fault Zones

Cottage destroyed by surface fault rupture on the Kekerengu Fault in New Zealand

Photo: Cottage destroyed by surface fault rupture on the Kekerengu Fault during the magnitude 7.8 2016 Kaikoura earthquake in New Zealand. Approximately 10 meters of right-lateral fault displacement occurred under this house, tearing it from its foundation. Photo credit: VML 190573, Julian Thomson, GNS Science / Earthquake Commission

Alquist-Priolo earthquake fault zones are regulatory zones surrounding the surface traces of active faults in California. (A trace is a line on the earth's surface defining a fault.) Wherever an active fault exists, if it has the potential for surface rupture, a structure for human occupancy cannot be placed over the fault and must be a minimum distance from the fault (generally fifty feet).

Earthquake fault zones were conceived in the Alquist-Priolo Earthquake Fault Zoning Act (Alquist-Priolo Act). The intent of the Alquist-Priolo Act is to reduce losses from surface fault rupture. California created this law following the destructive 1971 San Fernando earthquake (magnitude 6.6), which was associated with extensive surface fault ruptures that damaged numerous structures.

An active fault, for the purposes of the Alquist-Priolo Act, is one that has ruptured in the last 11,000 years.