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STANFORD -- The most detailed estimates in nearly a decade of the worst possible damage that could be caused by great earthquakes striking the San Francisco Bay, Los Angeles and Tokyo, Japan, have been completed by Haresh Shah, professor of civil engineering at Stanford, and associates at Risk Management Solutions Inc. (RMS) of Palo Alto.
According to the analysis:
These represent worst-case scenarios. They assume that the largest earthquakes considered likely to occur in the next 30 to 50 years strike as close as possible to the most highly developed areas in the three locations. They are the first such estimates released that take into account the experience from the 6.6 magnitude Northridge quake that struck Southern California last January 17.
Compared to similar analyses for San Francisco and Los Angeles made by the Federal Emergency Management Agency and the U.S. Geological Survey in 1981, the new figures show dramatically lower casualty figures and generally higher levels of property damage and economic loss, even when the older estimates have been adjusted upward for inflation, said Shah, Obayashi Professor of Engineering.
"These estimates reflect the fact that we have been pretty successful in engineering our structures to protect lives. We have now had several major earthquakes in California with remarkably few casualties. Each time we say that we were 'very lucky.' But you can't be 'lucky' every time," says Shah.
"On the other hand, with the losses from a moderate event like the Northridge quake mounting to more than $20 billion, we have clearly done a poor job at protecting property and functionality," he said.
The most dramatic example of this failure is the Tokyo case. The trillion-dollar economic cost of such an event is so great that it would seriously damage world financial markets as the Japanese withdrew their extensive overseas investments in order to rebuild, Shah says.
According to the engineers, the new analysis includes a previously underestimated source of economic loss, that resulting from the interruption of normal business. It finds that such losses could be comparable to the amount of property damage caused by ground shaking.
The Shah/RMS estimates are based on a new and potentially more accurate methodology than that used in previous studies.
In the past, such figures were prepared by doing detailed analyses of the buildings in several small but representative neighborhoods and then statistically generalizing the results of these small-scale studies to the entire area that would be affected.
Shah and RMS, however, have used a relatively new computer- mapping technology, called a geographic information system. It allows them to combine information about individual structures, such as their age, type and assessed value, with geological conditions, such as slope and soil type, that influence the behavior of the ground during an earthquake. In this fashion, they can estimate the amount of damage that every building and structure in an area might sustain if an earthquake of a given size occurs in a given location.
"Because it works with many of the largest insurance companies, RMS has developed the most significant database of its type in the world," said company president Tom Hutton.
According to Shah, having such a database is very important. "For any one house, we can easily be off by 100 percent. For 10 houses of the same type, we can do somewhat better. And for a thousand, we can do pretty well." Despite all the effort that goes into such estimates, however, uncertainties of less than 50 percent are considered quite good, he said.
One of the greatest areas of uncertainty in such analyses come from the attempt to translate predicted physical damage into dollar estimates. "If shaking causes a crack to develop in a wall, when can you fix it by just patching the crack and when do you have to replace the entire wall? There is no easy way to make such a determination in advance," Shah said.
Risk Management Solutions Inc. is a private company that evaluates earthquake risks for insurance companies. It was founded by Shah's son, Hemant. Hutton, the company president, is a past graduate of Stanford. Professor Shah is chairman of the board. The company licenses earthquake risk-assessment technology from Stanford, and the university holds stock in the company.
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