Each Quake’s Lessons Can Reduce Our Vulnerability : Risk reduction: But we have to commit the funds and choose lives over cost savings.

The Northridge earthquake has sharply refocused public opinion on seismic safety. Because such tragedies produce intense reactions, it is crucial that final judgments on the earthquake hazard in such megacities as Los Angeles should be based on the historical, seismological and engineering evidence.

What progress in earthquake mitigation has been made since the similarly damaging Sylmar temblor of 1971? Lives, property and industry have again been lost; why was more progress not made?

There are two main problems. First, the scientific understanding of earthquake generation, while significantly improved, is still seriously deficient in practical application. Pinpoint earthquake prediction is a distant dream. However, the geographical pattern of damaging, strong ground motion can now be more adequately forecast in areas where the basic geology is mapped, such as the Los Angeles and San Francisco Bay areas.

Second, competing social and economic forces prevent optimal growth and application of engineering knowledge for risk reduction. Not only is there substantial deficiency in spending what is necessary to remove or seismically upgrade structures; there is also indecision between the minimization of loss of life and the cost benefits of preventing economic loss.

Since the great 1906 San Francisco earthquake and fire, seismic risk mitigation in California has been guided by the objective of the Seismological Society of America: to ensure against damage by proper studies of earthquake geographical distributions, activities and effects on buildings. The Northridge earthquake demonstrates that substantial progress has been made but much fundamental work still needs to be done. Key seismological lessons have increased the safety of individuals, industrial plants and urban infrastructure. In the 1971 Sylmar earthquake, Olive View Hospital, built according to the then-current code and just open a month, was seriously damaged and later demolished. Last week, despite shaking similar to that recorded in 1971, the replacement hospital was not structurally damaged although operations ceased for a time. It met the minimum standards of the revised 1988 Uniform Building Code.

Similarly, most highway structures damaged last week were designed to meet pre-1971 requirements. A consequence of the 1989 Loma Prieta earthquake was legislation empowering Caltrans to retrofit high-priority bridges and overpasses.

The instrument recordings of recent California earthquakes have given the strength, duration and frequency of large seismic motions. These parameters are the essential ingredients for retrofit of old buildings and the seismic-resistant design of new structures. In the Jan. 17 earthquake, for example, strong motion records were obtained at a seven-story hospital in East Los Angeles that was constructed with large rubber pads (isolators) between the foundation and the structure. The records showed a significant reduction in the forces across the isolators.

The Northridge earthquake emphasizes the lessons of Loma Prieta that many crucial lifelines such as electrical power, water, sewage, communication and transportation remain unacceptably fragile. The severance of the San Francisco Bay Bridge in the 1989 earthquake dramatically made this point, confirmed again by widespread failure of lifelines in the Northridge earthquake. Nevertheless, such damage would have been even more widespread if sensitivity to the problem had not been raised by the earlier earthquakes.

People must consider all risks from earthquakes on an individual basis. There is thus an obligation in the assessment of the Northridge quake to explain the range of comparative risks to individuals, jobs and production. A persistent difficulty is the lack of agreement within our society about the highest priority goals of hazard abatement. Typically, legislators appropriate special funds immediately after disasters and propose many ordinances and bills. Experience indicates, however, that interest declines rapidly as the balance of risk from earthquakes and benefits from other actions comes into play. But despite the remaining prediction difficulties and the technical gaps in engineering, there are no insurmountable reasons why earthquake risks cannot be steadily reduced in a decade or so to levels comparable to those of more familiar threats.

We now proceed with the lengthy process of analyzing the Northridge earthquake and its aftermath. It is important to produce a checklist designed to help answer the question, “What if no actions had been taken in light of the 1971 Sylmar earthquake to reduce earthquake vulnerability?”