PASADENA- Can earthquake-proof buildings really be built? Researchers at the U.S. Geological Survey and the California Institute of Technology are busier than ever trying to determine why building collapse during earthquakes.

Researchers have learned much from the 1994 Northridge earthquake, which registered 6.7 on the Richter scale. One surprise result of the Northridge quake was the destruction of supposedly earthquake-resistant structures including steel-framed buildings and steel reinforced freeway overpasses. Similarly, in Kobe, many buildings thought capable of surviving an earthquake of that magnitude (somewhere between 6.5 and 7.0 on the Richter scale) failed to do so. Engineers would like to know what went wrong.

Thomas Heaton and colleagues from Pasadena's Earthquake Engineering Research Laboratory used computer modeling to test the effects seismic pulses from an 7.0 Richter scale earthquake on steel frame buildings built to the most recent California building codes. These studies showed that a seismic pulse similar to the maximum pulse of the Northridge quake, would have caused building to sway 35 centimeters on the lowest stories. This is three times more than is considered 'severe' by current definitions. These observations suggested a real 20-story building would have collapsed under such stress.

The researchers also ran similar simulations on buildings built on base isolated (rubber pad) foundations. This construction model, often used on hospitals and other critical buildings because of its earthquake resistant potential, also did not do well in modeling experiments. Although this style of structure fared better than the steel frame building model, it would take "exceptional measures" to design a base-isolated building that could survive a large earthquake, according to the study.

The greatest potential hazard involves older buildings, the researchers note. These include unreinforced and nominally retrofitted brick buildings and buildings made of nonductile concrete.

Building engineers are attempting to learn as much as possible about building earthquake resistant building by studying the steel remains of structures which rode out the Northridge quake. While, many of the buildings survived, instead of swaying as they were supposed to do, they developed significant cracks in key structural areas connecting horizontal beams and vertical columns. This suggests a strong need for new construction strategies. Earthquake specialists from the U.S., Italy and other countries are already en route to Kobe to study the damage to structures there.

The construction of earthquake resistant buildings depends on adequate knowledge of how the ground moves during major earthquakes. As new knowledge is gained with every earthquake, construction codes gradually change. However, much remains to be learned about this fundamental aspect of earthquakes before better buildings can be designed, notes Heaton.

Researchers have learned much from the Northridge earthquake, which registered 6.7 on the Richter scale. As bad as it was, the Northridge quake could have been worse, the scientists say, since the greatest amount of shaking in that quake was actually ten miles north of the epicenter in a less populated mountain area. Analysis of seismic recordings showed that seismic waves traveled north in the direction of the fault rupture, building up momentum as they traveled. The energy of that seismic pulse was at least twice as violent as that which shook Northridge, site of the epicenter.

It is possible that Kobe was on the receiving end of such a pulse. It is now known that the Kobe earthquake had a relatively shallow epicenter, about six miles deep. A shallow epicenter combined with close proximity to a populated area is a recipe for certain disaster. The Loma Prieta, which rolled through San Francisco and environs also had a shallow epicenter, and was of similar strength to the Kobe temblor.

Out of concern for earthquake risk, the Japanese have developed what are probably the most stringent construction standards anywhere. The most recent quake is bound to cause reconsideration of current standards.

The Kobe earthquake occurred without warning. Indeed only two major earthquakes in history have been successfully predicted using seismologic data (Haicheng, China in 1975 and Mexico in 1978). Research projects are now underway using satellites to monitor shifts in the earth's crust in an attempt to develop predictive models. Other research projects range from drilling mile-deep wells to measure hydrological changes and even observing the behavior of catfish and other animals.

Dr. Heaton's research appeared in Science, v.267, 1/13/95, pp. 206-211.

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