This is a partial transcript from "On the Record," Sept. 28, 2004, that has been edited for clarity.

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GRETA VAN SUSTEREN, HOST: Tonight, a major earthquake rocks California. Joining us on the phone from California is geologist Ross Stein. He's with the U.S. Geological Survey.

Ross, what happened in California today? And is there a risk of more aftershocks, even at this hour?

ROSS STEIN, GEOLOGIST: Well, we had what was only the most recent in a remarkable series of earthquakes, repeating earthquakes on an almost magical site on the San Andreas Fault. So it's the seventh in a series that began in 1857, with about 20 to 30 years separating each event.

VAN SUSTEREN: The San Andreas Fault is a very vulnerable point on the California coast. The fact that there was an earthquake today and the fact that there's been this 20-year interim period, does that give you any reason to feel comfortable tonight, or could it happen even tomorrow?

STEIN: Well, the chances of a larger earthquake tonight are much higher than they were last night because of the occurrence of this event. The earthquake struck in an unusual spot on the San Andreas, extending toward the San Francisco Bay area. The fault slips every day. It creeps. It doesn't store the stress necessary to produce large earthquakes, and we don't think that this earthquake will trigger anything extending toward the San Francisco Bay area.

But to the south, you know, toward the Los Angeles, this is the part of the fault that's locked, that's been storing stress for 150 years and that produced a magnitude 7.9 shock in 1857.

VAN SUSTEREN: All right, when that stress is released, you have the earthquake. What is it that causes stress to be released, for those plates to shift?

STEIN: Well, the plates are slowly being driven and they're basically hung up, like a stuck drawer in your dresser, on these faults. So eventually, the stress overcomes the resistance and bang: you have an earthquake. And the question that we're now focusing on is: What's the likelihood that this magnitude 6 could trigger a 7 or larger extending to the southland? And the answer is the chances are low. Perhaps in the next week, they're just a few percent. If we're thinking about a magnitude 6, maybe they're 10 percent.

But we also recognize that in 1857, that big earthquake was preceded nine hours beforehand by an earthquake just like the one we had this morning.

VAN SUSTEREN: All right. Did you have any notice that this earthquake was going to happen or is it the first time you discover it is when it happens?

STEIN: None whatsoever. And what's interesting about that answer is that in 1988, the USGS basically bet the farm on the thought that this earthquake was going to come, this magnitude 6. And so we instrumented it more richly than anywhere else in the United States and the date never showed up for the dance, which was a humbling experience for us. It's been 15 years we've been waiting.

But today turns that experience into a great investment for science because we captured this earthquake on a fantastic array of instruments. And we already know, at the level of one part per billion, there was not anything that happened immediately before this earthquake took place.

VAN SUSTEREN: All right, Ross. Thank you very much.

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