Glendale (PDF) - Hazard Mitigation Web Portal - State of California
Glendale (PDF) - Hazard Mitigation Web Portal - State of California
Glendale (PDF) - Hazard Mitigation Web Portal - State of California
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Natural <strong>Hazard</strong>s <strong>Mitigation</strong> PlanCity <strong>of</strong> <strong>Glendale</strong>, <strong>California</strong>SECTION 6:Section 6 – EarthquakesEARTHQUAKESWhy Are Earthquakes a Threat to the City <strong>of</strong> <strong>Glendale</strong>?While <strong>Glendale</strong> is at risk from many natural and man-made hazards, an earthquake is the event withthe greatest potential for far-reaching loss <strong>of</strong> life or property, and economic damage. This is true formost <strong>of</strong> southern <strong>California</strong>, since damaging earthquakes are frequent, affect widespread areas,trigger many secondary effects, and can overwhelm the ability <strong>of</strong> 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 <strong>California</strong>, recent earthquakes in or near urban environments have caused relatively fewcasualties. This is due more to luck than design. For example, when a portion <strong>of</strong> 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, <strong>California</strong>’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 <strong>of</strong> homes and businesses were without electricity; tens <strong>of</strong>thousands had no gas; and nearly 50,000 had little or no water. Approximately 15,000 structureswere moderately to severely damaged, which left thousands <strong>of</strong> 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 <strong>of</strong> fires after theearthquake causing additional severe damage. This moderately sized earthquake resulted in recordeconomic losses, and yet <strong>Glendale</strong> is at risk from earthquakes that could release more than ten timesthe seismic energy <strong>of</strong> the Northridge earthquake.Historical and geological records show that <strong>California</strong> has a long history <strong>of</strong> seismic events. Southern<strong>California</strong> is probably best known for the San Andreas fault, a 750-mile long fault running from theMexican border to a point <strong>of</strong>fshore west <strong>of</strong> 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 <strong>of</strong> the fault is considered a likely location for an earthquake within the next few decades. TheSan Andreas fault, however, is only one <strong>of</strong> dozens <strong>of</strong> known faults that criss-cross southern<strong>California</strong>. Some <strong>of</strong> 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, <strong>of</strong> <strong>Glendale</strong>, whereasthe lesser-known, but active Verdugo and Raymond faults extend through the central andsoutheastern portions <strong>of</strong> <strong>Glendale</strong> (see Map 6.1). Beyond these known faults, there are several“blind” faults that underlie southern <strong>California</strong>. [“Blind” faults do not break the surface, but ratheroccur thousands <strong>of</strong> feet below the ground. They are not less <strong>of</strong> a seismic hazard, though]. One suchblind fault ruptured causing the Whittier Narrows earthquake in October 1987. Each <strong>of</strong> these faultsis capable <strong>of</strong> producing, at a minimum, a moderate-sized earthquake that has the potential to inflictgreat damage on the urban core <strong>of</strong> 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 <strong>of</strong> southern <strong>California</strong>.Map 6.1: Faults In and Near <strong>Glendale</strong>2006 PAGE 6 - 2