Glendale (PDF) - Hazard Mitigation Web Portal - State of California

Natural Hazards Mitigation PlanCity of Glendale, CaliforniaSECTION 6:Section 6 – EarthquakesEARTHQUAKESWhy Are Earthquakes a Threat to the City of Glendale?While Glendale is at risk from many natural and man-made hazards, an earthquake is the event withthe greatest potential for far-reaching loss of life or property, and economic damage. This is true formost of southern California, since damaging earthquakes are frequent, affect widespread areas,trigger many secondary effects, and can overwhelm the ability of local jurisdictions to respond.Earthquake-triggered geologic effects include ground shaking, surface fault rupture, landslides,liquefaction, subsidence, and seiches. Earthquakes can also cause human-made hazards such as urbanfires, dam failures, and toxic chemical releases.In California, recent earthquakes in or near urban environments have caused relatively fewcasualties. This is due more to luck than design. For example, when a portion of the NimitzFreeway in Oakland collapsed at rush hour during the 1989, M W 7.1 Loma Prieta earthquake, it wasuncommonly empty because so many were watching the World Series. The 1994, M W 6.7Northridge earthquake occurred before dawn, when most people were home safely in bed. Despitesuch good luck, California’s urban earthquakes have resulted in significant losses. The moderatesizedNorthridge earthquake caused 54 deaths, more than 1,500 injuries and nearly $30 billion indamage. For days afterward, thousands of homes and businesses were without electricity; tens ofthousands had no gas; and nearly 50,000 had little or no water. Approximately 15,000 structureswere moderately to severely damaged, which left thousands of people temporarily homeless. Severalcollapsed bridges and overpasses created commuter havoc on the freeway system. Extensive damagewas caused by ground shaking, with shaking-induced liquefaction and dozens of fires after theearthquake causing additional severe damage. This moderately sized earthquake resulted in recordeconomic losses, and yet Glendale is at risk from earthquakes that could release more than ten timesthe seismic energy of the Northridge earthquake.Historical and geological records show that California has a long history of seismic events. SouthernCalifornia is probably best known for the San Andreas fault, a 750-mile long fault running from theMexican border to a point offshore west of San Francisco. Geologic studies show that over the past1,400 to 1,500 years, large earthquakes have occurred on the southern San Andreas fault at about130-year intervals. As the last large earthquake on the southern San Andreas occurred in 1857, thatsection of the fault is considered a likely location for an earthquake within the next few decades. TheSan Andreas fault, however, is only one of dozens of known faults that criss-cross southernCalifornia. Some of the better-known faults include the Sierra Madre, Newport-Inglewood,Whittier, Elsinore, Hollywood, and Palos Verdes faults. Of these, the Sierra Madre and Hollywoodfaults extend through the northern and southwestern portions, respectively, of Glendale, whereasthe lesser-known, but active Verdugo and Raymond faults extend through the central andsoutheastern portions of Glendale (see Map 6.1). Beyond these known faults, there are several“blind” faults that underlie southern California. [“Blind” faults do not break the surface, but ratheroccur thousands of feet below the ground. They are not less of a seismic hazard, though]. One suchblind fault ruptured causing the Whittier Narrows earthquake in October 1987. Each of these faultsis capable of producing, at a minimum, a moderate-sized earthquake that has the potential to inflictgreat damage on the urban core of the Los Angeles basin. For example, seismologists believe that a6.0 to 6.5 earthquake on the Newport-Inglewood fault would result in far more death anddestruction than a “great” quake on the San Andreas fault, because the San Andreas is relativelyremote from the urban centers of southern California.Map 6.1: Faults In and Near Glendale2006 PAGE 6 - 2