Archive for Wednesday, November 29, 1989


November 29, 1989


Having experienced the Oct. 17 California earthquake first-hand held Don Steeples, deputy director of the Kansas Geological Survey, in good stead when he gave a talk on earthquakes Tuesday evening.

Steeples, a seismologist, personalized a presentation on earthquakes with references to his own perceptions when an earthquake, measuring 7.1 on the Richter scale, rumbled through the San Francisco Bay Area.

Steeples spoke to about 10 people, mostly students and teachers, Tuesday evening in the Apollo Room of Nichols Hall at Kansas University.

Steeples was teaching seismology course in a Sunnyvale, Calif., motel, about 25 miles from the epicenter of the earthquake, when the ground beneath him began to move. He said that for a few minutes after the earthquake struck, he was a little worried.

"For a couple seconds, I was concerned I wasn't going to be able to get out of the building," he said.

BUT AFTER he was outside, Steeples said that watching and feeling something he had studied many years made the experience very interesting.

"I was able to enjoy it," he said. "I was able to recognize waves as they came though."

Steeples said the waves were caused by pulses of energy traveling outward from the center of the earthquake. The surface waves that come a few seconds after the initial, deeper waves cause the most damage to structures.

"Surface waves make it very difficult to walk," he said.

In his talk, Steeples, 44, said earthquakes were caused by huge layers of rock rubbing against each other, and talked specifically about various earthquake zones around the world, especially those in the United States.

AS FOR THE recent California earthquake, Steeples said it was "a bit ominous" because there was very little seismic activity before it hit.

Because many earthquake experts believe that earthquakes historically have been followed by more seismic activity, Steeples suggested that another earthquake of the same magnitude may hit the Bay Area soon.

Much of Steeples' talk focused on the power that is inherent in an earthquake. He showed numerous slides of rock that was split open during an earthquake.

"When the first rock breaks, the breakage promulgates along the fault at a mile per second," he said. "It goes until the energy is not sufficient to break rock."

Steeples's discussion of an area close to Kansas, the New Madrid fault zone in southeast Missouri and northeast Arkansas, brought questions from an interested audience.

STEEPLES said that based on records from major earthquakes in this area in the early 1800s, an earthquake today probably would not cause too much damage in Kansas City. But the same is not true of the St. Louis and Memphis areas, Steeples said.

"The Memphis area, a good part is built on a flood plain," he said, adding that the area "will shake like a bowl full of Jell-O. That's a major concern."

Frank Wilson, a geologist with the Kansas Geological Survey who was in the audience, said that not much has been done in Memphis to prevent extensive damage from a quake along the New Madrid fault. He said St. Louis has done more preparation.

In response to another question, Steeples said the odds of an earthquake measuring over 8.0 on the Richter scale, such as the one that hit San Francisco in 1906, is unlikely.

STEEPLES said he based this opinion on several factors, including the fact that the return rate of that large an earthquake is between 190 and 400 years.

Also, he said, the amount of pressure on the fault was three times greater in 1906 than it is now.

But Steeples said an earthquake the strength of the one Oct. 17 is much more likely.

"You could have three or four or a half-dozen of those in 100 years," he said.

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