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Earthquakes in California

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Earthquakes in California are certainly not a surprise. What is a surprise is their unpredictability and randomness. Geologists say there is roughly a 50 percent chance that a magnitude 8 or more quake will hit the Los Angeles area sometime over the next 30 years. And, over the past twenty years, the Los Angeles area has witnessed several earthquakes, and in particular, two that were quite devastating; the 1971 San Fernando earthquake, and the January 17, 1994, Northridge Earthquake. Given the certainty that earthquakes will occur, they still seem to come as a surprise, and leave many communities unprepared to deal with their aftermath.

On October 1, 1987, at 7:42 a.m. the residents of the Los Angeles basin got a jolting reminder of the perils of "living on the fault line." This was due to the so-called Whittier Narrows earthquake. Hardest hit by the quake, was Whittier (pop. 72,000). Whittier is twelve miles from downtown Los Angeles and was the community closest to the epicenter.

When the quake, registering 6.1 on the Richter scale, first struck, it was thought to be centered along the Old Whittier Fault. However, after extensive study, it was determined that it was actually the result of a "new" fault, or a fault that had not previously been discovered by scientists.

What are the lessons learned from the Whittier quake? And, how does this quake compare to other more recent, higher magnitude quakes? Despite the fact that regular warnings are part of California living, repeated in schools, in earthquake exercises, by local and state governments, and even in the front of telephone books, many people were caught off-guard and panicked. Fortunately, Californians learned a lot from the Whittier quake.

The Whittier earthquake was not the "big one" that Angelenos perpetually wait for. This may be hard to comprehend given the extensive damage caused by the earthquake. Although classified as "moderate," the quake left more than 100 injured and six dead, including an electrical repairman buried in an underground tunnel, a college student struck by falling concrete in a campus garage, and three people who died of heart attacks brought on by the shock.

As a spokesman for the city of Whittier put it, the crumbled business district "looks like downtown Beirut." (Kerr, 16). Twenty buildings there were condemned and over 2000 homes were damaged. According to Magnuson, "Eight blocks in Whittier's business district were closed after bricks cascaded on cars, and at least eight buildings were too damaged to be saved" (Magnuson, p. 32). It is estimated that the Whittier Narrows earthquake caused over $358-million in damage.

The practical lessons learned from this quake seem to be the same as those learned in both previous and subsequent earthquakes. Among them is the necessity for earthquake preparedness. This was identified, and mandates were developed, before the 1987 Whittier quake. The California Earthquake Hazards Reduction Act of 1986 was enacted to direct the Seismic Safety Commission to establish a series of five-year programs to reduce state-wide earthquake hazards significantly by the year 2000. The first program became the States' official earthquake hazard mitigation program (The Commission, p. 1).

The quake was also a lesson to those who have long ignored the warnings about the hazards posed by old, unsafe, masonry buildings. In 1933, unreinforced masonry was banned in new construction, after 130 people were killed by a 6.3-magnitude earthquake. However,

thousands of pre-1993 buildings had not been earthquake-proofed when the 1987 Whittier quake hit (Magnuson, p. 32).

This was despite the fact that there had been a 1992 deadline in place to ensure that all buildings were earthquake-proof. Building damage by the quake confirmed the value of ongoing efforts to improve the seismic resistance of these buildings, and increased efforts were made towards enforcement of these building codes.

Since the earthquake however, buildings throughout California, and particularly Southern California have continued to be "retrofitted" or made more earthquake-proof. However, the process is slow, "Remedial strengthening of buildings in the City of Los Angeles is progressing, but such efforts are slow or absent elsewhere in the region" (Kerr, p. 270).

Not only were practical lessons learned from this quake, but scientific ones as well. For example, after subsequent weeks of analysis of seismic data, the epicenter was pinpointed several miles northwest of the end of the Whittier fault. Additionally, the quake's motion was indicative not of a strike-slip, but of thrust faulting, meaning that slippage along a thrust fault hidden deep below the surfaced had triggered the quake. (Horgan, p. 21). What scientists had discovered is that we are at risk from not just "major" faults, but smaller folds near the earth's surface that seem to mark regions threatened by earthquakes. According to Dr. Lucy Jones of the U.S. Geological Survey in Pasadena, "thrust faults underlying Los Angeles probably cannot create quakes with a magnitude greater than 6.5 or 7. But she suggests that such earthquakes originating directly under the city, could prove more devastating than an 8 magnitude quake along the San Andreas fault, which passes some 35 miles northwest of the city" (Horgan, p. 18). This information could prove vital in predicting or forecasting earthquakes.

Since the 1987 Whittier Narrows earthquake there have been even larger, more devastating earthquakes, that repeated many of the same warnings. For example, Californians learned even greater lessons from the October 17, 1989, Loma Prieta earthquake, or as its commonly known, the San Francisco earthquake. Although larger than the 1987 Whittier earthquake, the quake which measured Magnitude 7.1, is still considered of moderate size. It is believed to have re-ruptured the southernmost 25-mile segment of the 1906 San Andreas fault break. The epicenter was approximately 11.5 miles deep on the San Andreas fault. This deepness and location along one of California's largest faults, is where it differs from the 1987 Whittier quake.

In addition, it caused even more damage than the Whittier quake. The Loma Prieta earthquake resulted in approximately $10-billion in direct damage and indirect losses. There were 63 deaths and 350 hospitalized injuries (California Seismic Safety Commission, p. 1). The most devastating loss of life occurred when the I-880 Cypress Street viaduct collapsed. It took 43 lives.

As in the Whittier quake, many older buildings of types known to be vulnerable suffered major structural failures. In total, over 24,000 residential structures, 3,500 commercial buildings



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