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Earthquakes: Improving the Odds for Survival
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17769 |
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Section : |
NATURAL SCIENCE
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| Issue
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6 / 1990 |
2,229 Words |
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Ian G. Buckle
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Of all the natural hazards that are experienced around the world, perhaps the most terrifying and unforgiving is the large-magnitude earthquake. It is terrifying because it occurs without warning and catches people unprepared. It is unforgiving because it searches out every structural weakness and societal flaw without mercy. Certainly the continuing struggle to survive these "rapid onset disasters" has led to a better understanding of earthquakes, but every year hundreds of people are killed and property is damaged and destroyed by them.
In fact, more people are at risk today than even a decade ago due to the explosive growth of metropolitan centers in seismically hazardous regions. Furthermore, the infrastructure necessary to sustain this growth is struggling to keep up with the demand, and earthquake protection is, in many cases, the lowest item on the priority list.
Recent damaging earthquakes in Mexico City, Armenia, and Northern California have highlighted the vulnerability of the built environment. Collapsing buildings and bridges have killed and injured people. Earthquakes have ruptured pipelines, started fires, and disrupted and destroyed businesses. The emotional scars have taken longer to heal than the physical ones. Some people have never recovered.
But unlike a nuclear war or other manmade disaster, earthquakes cannot be prevented or resisted. Engineers cannot build earthquake-proof structures. Instead, building codes target life safety as the primary and only objective, with structural damage acceptable provided lives are not lost. Arm wrestling with a major earthquake is not a winnable proposition; instead, we strive to be clever enough to avoid a head-to-head battle of strength while still ensuring life safety.
History tells us that we are not always as clever as we would like to think we are. The Loma Prieta earthquake in California last October was only a moderate earthquake some 60 miles away from the cities of San Francisco and Oakland. Even so, more than 60 people died and the cost of repair and rehabilitation of the infrastructure is expected to exceed $10 billion.
The reduction of our vulnerability to earthquake hazards is one of the most pressing challenges of our time, needing to be shared by engineers, social scientists, emergency response officials, and state and federal governments. It also must be approached internationally.
Fence or Ambulance?
To put the issues surrounding earthquake hazard mitigation into perspective, it is helpful to ask the question, "Is it better to build a fence at the top of a cliff or to station an ambulance at the bottom?" In the earthquake hazard field, it is clear that we should do both because we do not know how to build a fence with sufficient strength and affordability to meet all contingencies. Likewise, engineers know that it is unrealistic to resists earthquake forces head-on. The fence designer is satisfied if he can keep the truck on the cliff's highway, and he accepts the fact that the fence will be badly bent out of shape on impact. The fence and truck may even have replaced, but lives will be saved. This is the central concept of life safety and acceptable damage. These are very special fences - they must be able to absorb heavy impact without fracture.
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