Abstract

The Alquist-Priolo Earthquake Fault Zoning (AP) Act was passed in California in 1972 following the destructive 1971 Mw 6.6 San Fernando earthquake. Surface-fault rupture hazard is addressed by prohibiting most structures for human occupancy from being placed over the trace of an active fault. Principal responsibilities under the AP Act are assigned to the following: 1) State Mining and Geology Board (SMGB), 2) State Geologist (California Geological Survey), and 3) lead agencies. The SMGB establishes specific regulations to guide lead agencies in implementing the law. The AP Act requires the State Geologist to issue maps delineating regulatory zones encompassing potentially hazardous faults that are sufficiently active (active in approximately the last 11 ka) and well defined. The first maps were issued in 1974—currently there are 547 maps affecting 36 counties and 104 cities. Lead agencies affected by the zones must regulate development “projects” in which structures for human occupancy are planned within the Earthquake Fault Zones (EFZs). Significant events in the history of the AP Act include A) the establishment of the Fault Evaluation and Zoning Program in 1976 (which also initiated the change from zoning faults with Quaternary displacement to those with Holocene displacement); B) the publication of the Reitherman-Leeds study in 1991, which evaluated the effectiveness of the AP Act; C) earthquakes associated with surface-fault rupture since the AP Act was passed, especially the 1992 Mw 7.3 Landers and 1999 Mw 7.1 Hector Mine events; D) release of digital versions of EFZ maps, Fault Evaluation Reports, and site investigation reports in 2000–2003; and E) the appeal to SMGB by the City of Camarillo, resulting in the establishment of the SMGB's Technical Advisory Committee.

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