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THE MORE YOU KNOW, THE BETTER PREPARED YOU'LL BE Earthquakes are inevitable in California. We can't predict or prevent them, but we can reduce their physical and psychological impacts. By understanding the risk they present and what we might face in their aftermath we can better prepare. A moderate or major earthquake in a densely populated area could cause a considerable number of deaths and injuries and millions of dollars in property losses. It also could severely impact transportation, water, electrical and other lifeline systems upon which we depend. This topic provides a general overview of the seismic risk in Southern California and the general problems our communities might face after a damaging earthquake. Understanding this information is the first step in preparing to respond when the next earthquake strikes. THE THREAT IN SOUTHERN CALIFORNIA When many Southern Californians think of earthquakes, they think of the so-called "Big One," a magnitude 7 or larger event on the San Andreas fault. The San Andreas is the most prominent fault in the region. It is divided into the northern, central and southern sections. The central and southern sections stretch from Cholame in northeastern San Luis Obispo County to the Salton Sea in Imperial County and are broken into five segments: the Cholame, Carrizo, Mojave, San Bernardino Mountains and Coachella Valley. Because the San Andreas is the longest fault, it is capable of producing the largest earthquakes. The last earthquake on the southern San Andreas occurred in 1857. Scientists believe the fault ruptured at an area close to Parkfield in southern Monterey County and extended to Cajon Creek in San Bernardino County. Its magnitude is estimated at 7.8. The 1857 earthquake did not extend onto the San Bernardino Mountains and Coachella Valley segments. Scientists estimate that the last earthquakes on these segments occurred in 1812 and 1690, respectively. An earthquake on the San Andreas could cause considerable deaths, injuries and property losses, particularly in the areas closest to the fault rupture and in areas with poor soil conditions. But it isn't the only fault that threatens southern Californians. OTHER FAULTS Scientists estimate that more than 200 faults in the area can generate a magnitude 6 or larger earthquake. Among them are the Cucamonga, Elsinore, Elysian Park, Garlock, Imperial, Newport-Inglewood, Palos Verdes, San Jacinto and Sierra Madre Faults. Recent seismic events have shown that earthquakes on faults other than the San Andreas can cause a considerable number of casualties and a significant amount of property damage. The 1994 Northridge earthquake (magnitude 6.7) occurred on a previously unmapped thrust fault. The trembler caused 57 deaths and more than 9,000 injuries. Estimated property losses are $20-25 billion. POSSIBLE IMPACTS IN YOUR AREA Impacts of the Northridge earthquake included: Loss of electricity: An estimated 2.6 million people in Los Angeles and nearby cities and an additional 150,000 customers who were tied to the power grid from other states lost electrical service. Although electrical service resumed for 900,000 customers by dusk, it took more than a week to totally restore service. Damage to water systems: All four pipelines that transport water from northern California to the San Fernando, Simi and Santa Clarita valleys and supply three water treatment plants were affected. In addition, more than 1200 water line leaks in the San Fernando Valley and 300 in the Santa Clarita Valley were discovered after the earthquake. As a result, it was late January or early February before water service resumed in some areas. Damage to transportation systems: Several bridges, overpasses and freeway structures suffered damage in the earthquake. Included among them were the 15-Antelope Valley Freeway interchange, the Santa Monica Freeway over Fairfax Avenue and Venice and La Cienega boulevards as well as the Simi Valley Freeway over Balboa and San Fernando Mission boulevards. Impact on fuel supply systems: The earthquake caused an estimated 490 breaks and leaks in gas distribution lines, 40 in transmission lines and 860 in service connection lines. The trembler also caused 1400 breaks and leaks in the piping system. A magnitude 6 or larger earthquake on any of the other faults in the area could have similar, if not greater, impacts on these and other systems, particularly if it occurs in a densely populated and industrialized area. RESOURCE Additional information on the earthquake threat is available in "Putting Down Roots in Earthquake Country," which was published by the Southern California Earthquake Center (SCEC) and is available at libraries throughout Southern California.