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The Seattle Earthquake

February 28, 2001 at 12:00 AM EDT
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GWEN IFILL: The quake hit at 10:55 AM Pacific Time and was felt as far as 300 miles away from its epicenter. Damage assessment is ongoing. For what we know about the quake so far, we are joined by Randall Updike, chief scientist for the geologic hazards team at the U.S. Geological Survey in Colorado.

Mr. Updike, people who were on the West Coast today in Portland and Seattle and Olympia, Washington said that the ground under their feet felt like Jell-O. Exactly what is the magnitude of a 6.8 earthquake? What does that mean?

RANDALL UPDIKE: Well, this is a pretty important earthquake. Magnitude 6.8 in that part of the United States only occurs maybe every 25 years or so. And so this is very significant, most of the people in that part of the world have never felt an earthquake of this magnitude.

GWEN IFILL: When we look at the results, the pictures that have come from there and we begin to see rubble — we see bricks falling — we see broken glasses; we some isolated fires. You know, you get a helicopter in there and you can see a lot of the damage. But what is unclear to us when we look at all of this is we compare it to what we know. And what Americans know is California earthquakes like the Northridge earthquake, and this one is similar magnitude yet it appears at least at first blush that it is not as damaging.

RANDALL UPDIKE: That is correct, Gwen. The most important difference here is that the earthquake occurred about 60 kilometers below the surface.

GWEN IFILL: Which is about how much – about 30 miles?

RANDALL UPDIKE: About 40 miles, yes, below the surface, which is quite a bit deeper than the quakes in California. In addition, the earthquakes in California often occur very close under populated areas, and they occur in rocks that strongly amplify the earthquake waves. In the Seattle area, it’s, it’s less so.

GWEN IFILL: What are the, there are plates which, the way we’ve understood it is that plates rub up against each other and earthquakes happen. What is it about the geologic makeup in that area that caused this quake to happen?

RANDALL UPDIKE: Yes. Well, we’ve been studying this particular region of the United States for a couple of decades now very intensely because we know that what is called the Juan de Fuca Plate, which is out in the North Pacific Ocean, is converging with North America and is actually being subducted or sliding beneath North America. And as that convergence and sliding occurs, then earthquakes can be generated along the contact and those earthquakes can be quite large, very large. In fact, some of the largest earthquakes in the world have occurred along this kind of a geologic environment.

GWEN IFILL: Is this something that happens frequently in the Pacific Northwest?

RANDALL UPDIKE: There again, we’ve been doing studies that have indicated that earthquakes actually much larger than the one we witnessed this morning have occurred in the past in the pacific northwest. So there is a record even in the past few hundred years of significantly large earthquakes. Earthquakes like the one that occurred today have occurred other times in the 20th century.

GWEN IFILL: We’ve also heard that this one was felt as far, 300 miles away — in Portland — It was felt in British Colombia. Is the depth of the earthquake related to how wide a quake was felt in this case?

RANDALL UPDIKE: That is a very good question. Part of the reason is the depth. Also the magnitude and the orientation of the failing or slipping surface and the fact that the rocks in the Pacific Northwest can transmit that energy over large distances. We have reports that it was felt as far away as Salt Lake City.

GWEN IFILL: What about the potential for aftershocks?

RANDALL UPDIKE: Actually, we are monitoring very closely and the aftershock pattern is very weak. We are not seeing many events. This is also not too much of a surprise because this type of a deep subduction zone earthquake generally doesn’t produce abundant aftershocks. This doesn’t mean, however, that we shouldn’t be prepared to see some significant aftershocks and people that are responding to this earthquake should be very careful in where they are located and staying away from walls or other objects that could fall in an aftershock.

GWEN IFILL: You are saying the danger is still not passed necessarily.

RANDALL UPDIKE: That’s correct.

GWEN IFILL: You are going to send investigators from the Geological Survey to take a look at this. What are they going to be looking for and what are you hoping to learn?

RANDALL UPDIKE: That’s correct, Gwen. In fact, we have people in the air right now with equipment deployed and they are going to be flying into Portland tonight. I’ll have about 14 people from the USGS there by tomorrow night. The objectives are to monitor the aftershocks, to monitor how the ground is responding in various parts of the region — the idea being to help us understand and forecast in the future and thereby reduce the future hazard from earthquakes. In addition to monitoring the ground shaking we’ll also be looking at some of the other effects from the earthquake including landslides and a phenomenon that we call liquefaction in which sandy deposits that are shaken very strongly can actually lose their bearing strength and buildings or other structures on those soils can actually sink into the ground.

GWEN IFILL: Is it fair to assume that even though these kinds of earthquakes may not be preventable they might be predictable?

RANDALL UPDIKE: We are a long ways from predicting. But we are in the mode of trying to forecast future earthquakes. In other words give probability similar to the way the Weather Service gives forecasts of weather tomorrow. They don’t predict that it’s going to rain in a particular area. They give you a forecast of probability that it will rain. And that is what we are attempting to do with earthquakes.

GWEN IFILL: Randall Updike, thank you very much for joining us.

RANDALL UPDIKE: A real pleasure, thank you.

 

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