WASHINGTON — Construction of homes, schools, offices and shopping centers would be subject to more stringent guidelines for earthquake resistance if new federal safeguards are incorporated into local building codes, government officials said here last week.
The guidelines, drawn by the Federal Emergency Management Agency, mark the first time that a national code for seismic building construction has been formulated, agency spokesman Gary Johnson said. They are scheduled for widespread distribution in June as potential patterns for updating local building codes.
If adopted by local governing bodies as amendments to the existing Uniform Building Code, the proposals would raise the minimum acceptable limits of earthquake force that new structures would be required to withstand and improve acceptable design and construction techniques at an estimated increase of about 2% in building costs.
Meanwhile, recent geologic changes along California's fault lines have prompted the 14-member National Earthquake Prediction Evaluation Council to conclude that "gathering additional critical data is of very high priority."
In a summary of recommendations to be sent to the U.S. Geological Survey in June, the council will propose a series of steps to enhance data collection. They include increasing the number of seismic instruments along fault lines and spacing them closer together; measuring and dating soils, and digging "fault trenches" to identify and measure newly discovered faults.
"They (scientists) have noticed changes and are trying to look at what these changes might mean. There is a seismic network in place, but it could be improved by making the network a little bit denser," said Clem Shearer, of the U.S. Geological Survey.
Geologic instruments placed along fault zones have recently registered slow motions of the earth known as "slip" and "tilt," and scientists are predicting that a major earthquake will occur in California within the next 30 years, Shearer said.
"The consensus of the council is that there is a significant threat to the highly populated areas of the San Francisco Bay Area from smaller earthquakes," Shearer said.
Richard Krimm of the Federal Emergency Management Agency cites "irresponsible building practices" that put more than 6,000 structures situated along San Francisco Bay at "significant risk" from even small temblors.
Many of the structures, built before 1973 atop sandy soil, are expected to absorb the most intense earthquake shock waves. The soils are similar to those found in areas that sustained the worst damage in Mexico City's devastating earthquake in September.
Sections of the existing Uniform Building Code that provide regulations for seismic safety are currently undergoing a major revision by the International Conference of Building Officials and may incorporate many of the federal provisions or similar proposals submitted by a group of California engineers.
While differing in approach to building design, the two proposals would result in the same degree of building protection at about the same cost, according to the building officials group.
Expected to be completed by 1988, changes in the existing code will affect only new construction and will require buildings to be "flexing, bending, and non-brittle so that they will be able to go through several cycles of bending without collapse," if approved by local jurisdictions, said Richard Eisner of the Bay Area Regional Earthquake Preparedness Project.
"If the federal guidelines are implemented as part of the new Uniform Building Code, it will result in a significant upgrading in the quality of new construction along the bay," Eisner said.
"The real problem we have is that development decisions are often economic and political. The problem we need to address is not only getting the codes revised, but making sure the decision-makers know that the risks exist," he said.
The Whittier-based International Conference of Building Officials is also developing a nationwide code for retrofitting existing buildings that are earthquake-prone. Approval by local government officials would be required to make the code mandatory.
Focus of Code
Much of the code will focus on structures with unreinforced masonry that were built before 1934. More than 8,000 such buildings exist in Los Angeles and retrofitting to make them earthquake resistant will cost between $5 and $10 a square foot, according to the building officials.
The present code, formally titled the "Uniform Code for Building Conservation," would require an analysis of each individual structure to determine the extent of retrofitting and could be in place by 1987 for use in the West and Midwest, officials said.
While earthquakes in the United States occur most frequently west of the Rocky Mountains, more than 70 million people in 44 states are at risk from moderate to severe episodes, experts say.