LOS ANGELES — George Housner, who pioneered the modern field of earthquake engineering, developing the most complete mathematical system to analyze the effects of ground-shaking on structures, has died. He was 97.

Housner, the Braun Professor of Engineering, emeritus, at the California Institute of Technology, died Monday of natural causes at a Pasadena rest home.

His interest in earthquake engineering was spurred by the March 10, 1933, earthquake in Long Beach, which was later estimated at 6.3 on the Richter scale. Brick buildings with unreinforced masonry walls, including many school buildings, failed catastrophically. Although 120 people were killed, the loss of life would have been much worse if the quake, which hit at 5:55 p.m., had struck during school hours.

According to Tom Heaton, professor of engineering seismology at Caltech and a former colleague of Housner, the state of earthquake engineering hardly existed at the time.

“Nothing was mentioned in engineering books regarding designing to resist earthquakes,” Housner told the Los Angeles Times in a 1999 interview.

At the most, Heaton said, engineers considered only how a building would fare in a quake by calculating the force of the pushing on it. It took Housner to realize that an earthquake “is not static” but set off vibrations throughout the entire structure that could bring it down. Housner developed the mathematical framework to understand those vibrations, which led to the implementation of more rigorous building standards nationwide, Heaton said.

To many in the field, Housner is known as the father of earthquake engineering, a vigorous subdiscipline of civil engineering.

“George was a man of great intellect, which he used diligently to reduce the impact of earthquakes on our society,” Heaton said. “He was one of those people who changed our world.”

In 1988, President Ronald Reagan gave Housner the National Medal of Science, recognizing “his profound and decisive influence on the development of earthquake engineering worldwide. His research contributions have guided the development of earthquake engineering and have had an important impact on other major disciplines.”

According to Heaton, even after his retirement, Housner continued to show up each day at his Caltech office. Heaton recalled the time in the late ’90s when he was about to give a lecture on a particularly thorny topic and was having trouble mastering it.

“George was walking by my office,” Heaton said, “so I asked his advice.”

“It’s been a long time since I thought about that,” Housner said, and walked off.

“Five minutes later, he came back, picked up the chalk and wrote out the whole answer,” Heaton said. “I thought, Wow. He was 88 at the time.”