BOX 3.2 Fault Rupture and the Alquist-Priolo Act
Surface breaks did not receive serious attention as a seismic hazard until the 1971 San Fernando earthquake, when a fault ruptured a densely populated area of Los Angeles, destroying almost 100 structures. California responded in 1972 with the Alquist-Priolo Special Studies Act, which prevented construction of new buildings for human occupancy across an active fault. For existing residences on a fault, real estate agents were required to disclose the information to potential buyers. Notably, the act did not cover publicly owned facilities, critical facilities and lifelines, or industrial facilities, many of which contain hazardous materials.
The act required the state geologist to initiate a broad, and continuously updated, program of seismic hazard mapping to define the fault zones. “The earthquake fault zones shall ordinarily be one-quarter mile or less in width, except in circumstances which may require the State Geologist to designate a wider zone … The State Geologist shall continually review new geologic and seismic data and shall revise the earthquake fault zones or delineate additional earthquake fault zones when warranted by new information.” The California Division of Mines and Geology issues fault-zone maps at a scale of 1:24,000.
In 1990, California enacted the Seismic Hazards Mapping Act, which significantly broadened the responsibilities of the state geologist beyond the Alquist-Priolo zones by requiring that landslide and liquefaction hazards be mapped throughout the state. Funds for this program are provided by FEMA from mitigation resources authorized by the Stafford Act and fees from construction building permits.
gram of highway bridges in California that was greatly accelerated by the dramatic bridge failures (e.g., the Interstate 880 Cypress Viaduct in Oakland, the upper deck [east-to-west] crossing of the Oakland-San Francisco Bay Bridge, and the Struve Slough Bridge near Monterey) caused by the 1989 Loma Prieta earthquake.
Bridge seismic retrofits in California from 1971 to 1989 were limited to a cable-restrainer installation at hinges between adjoining bridge segments to prevent the ends of the spans from falling off the support seats. After the Loma Prieta earthquake, the retrofit program was broadened to include bridge columns and footings. Based on focused research, novel yet practical schemes, such as wrapping columns with steel collars or fiber-reinforced composite materials, were implemented on many vulnerable bridges to improve their seismic performance.
A notable aspect of the U.S. experience in achieving life safety is the consensus on the standards and practice for earthquake-resistant design established through the efforts of private, nonprofit organizations. Among the most important are the Structural Engineers Association of California, the Building Seismic Safety Council (BSSC) (84), the Applied Technology Council (ATC) (85), the Earthquake Engineering Research Institute (86), and the American Society of Civil Engineers (87). Backed by state and