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March 25, 2014 at 2:11 PM

UW seismometers record slide sequence

seismo01

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A seismometer about 7 miles from Saturday’s landslide recorded the ground rumbling as the hillside gave way.

The instrument, at Jim Creek, picked up the initial slide at 10:37 am. The signal lasted about 2.5 minutes and probably represents the movement of the landslide mass that had sloughed off in 2006 and was lying at the base of the slope,  said University of Washington seismologist Kate Allstadt. It was that pile of soil, rocks and water that surged across the river and buried homes and roads.

A few minutes later, a second rumble shook the ground as the upper reaches of the slope gave way.

Small pulses over the next several hours probably represent smaller slides and debris falling off the slope, Allstadt said.

The scientists also noticed several spikes before the landslide, which they initially thought might represent precursory cracking and shifting within the hill. But the regular nature of the spikes and the fact that they appeared  on previous weekends indicate some type of human activity, not ground motion.

However, Allstadt plans to examine the signals more closely for any early indications that the hillside was deforming. She also hopes to use the seismic data to calculate the size of the slide and the force it exerted as it dropped off the hill.

More coverage of the mudslide can be found here.

Comments | More in General news | Topics: ground motion, landslide, Oso mudslide


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