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7/28/2005 Jeremy Pearce from the New York Times

Bruce A. Bolt, a seismologist who made important observations about earthquakes in California and later helped translate the research into safer and more resilient bridges and buildings, died on July 21 in Oakland, Calif. He was 75.

The cause was pancreatic cancer, his family said.

From 1963 to 1991, Dr. Bolt directed the Berkeley Seismological Laboratory, which maintains a network of about 25 broadband seismometers in California and Oregon to measure the earth's movements along the San Andreas fault and other seismic features.

Dr. Bolt examined variations in waves recorded by the seismometers and was an early proponent of making digital recordings on tape, instead of paper, to allow for computer analysis. He studied the deep-earth sources of earthquakes and coined the more graphic term "fling" for a phenomenon scientists call elastic rebound, which occurs along a fault line in an earthquake's initial stages. It is this snap-back along a slipping fault, much like the rebound of a rubber band, that causes much of the damage to structures after a quake.

In 1975, Dr. Bolt and Toshi Asada, a Japanese seismologist, led a study of the Gorda Basin, off California's northern coastline. Using a string of underwater seismometers, the team recorded frequent small earthquakes, as many as five per hour, and a surprising level of seismic activity near the San Andreas fault.

In the 1980's and 90's, Dr. Bolt encouraged a more rational public response in preparing for the likelihood of major earthquakes. He served as chairman of the California Seismic Safety Commission and made the point that "by using physics and mathematics, you can study the forces that govern earthquakes to improve earthquake-resistant designs for public structures," said Douglas S. Dreger, an associate professor of geophysics at the University of California, Berkeley.

Dr. Bolt advised on the strengthening of the Golden Gate Bridge and studied the destructive San Francisco earthquake of 1906 in making recommendations to engineers for improving the resilience of the city's buildings. He also conducted ground-motion studies for the designs of dams, oil pipelines, nuclear reactors and underground train systems.

He wrote two popular books, "Inside the Earth: Evidence from Earthquakes," in 1982, and "Earthquakes: A Primer," first published in 1978; its fifth edition appeared in 2003. Both were published by W. H. Freeman.

Bruce Alan Bolt was born in Australia in Largs, New South Wales. He earned his doctorate in applied mathematics from the University of Sydney in 1955.

Dr. Bolt was named a professor of seismology at Berkeley in 1963 and remained there until retiring in 1993. He served as president of the Seismological Society of America from 1974 to 1975.

He was a former president of the California Academy of Sciences. In 1987, Dr. Bolt was elected an associate of the Royal Astronomical Society. He became an American citizen in 1972.

Dr. Bolt is survived by his wife of 49 years, the former Beverley Bentley, a mathematician who contributed to his earthquake studies. The couple lived in Berkeley. He is also survived by a son, Robert of Hillsborough, Calif.; three daughters, Margaret Barber of Rumson, N.J.; Helen Bolt Juarez of Fremont, Calif.; and Gillian Bolt Kohli of Wellesley, Mass.; a sister, Fay Bolt of Sydney, Australia; and 14 grandchildren.