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Quake Tahoe? Researcher Studies Faults Under The Lake



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(Lake Tahoe)
Monday, June 27, 2011
I feel a little like I'm on vacation, out on a boat in the middle of Lake Tahoe famous deep blue waters on a calm beautiful day. But I'm actually  here with a team of seismologists on a serious mission. They're  looking for clues about when the next big earthquake could strike the Lake.  
 
I'm sure a lot of beachgoers this summer would have a hard time imagining a devastating earthquake churning up these placid waters. But as Graham Kent who heads up University of Nevada at Reno's seismological lab explains calm waters belie a violent past. 
 
Graham Kent: "We're heading right for the largest fault in the basin, the west Tahoe fault ruptures about every four to five thousand years. It's last rupture was 4500 years ago. So obviously there's some concern because we're at the end of that earthquake cycle.  Doesn't mean it's gonna happen tomorrow.  But it wouldn't be a surprise if it did."
  
At least three faults run underneath the lake: the Stateline, the Incline Village and the West Tahoe.  Now it looks like there is one more. 
 
Graham Kent: "Yesterday we discovered there's a smaller fault in between the West Tahoe and the Stateline.  So that's one of the things we just found out yesterday."
 
To help get answers like that, Kent is deploying a cutting edge tool he and his team developed. It looks like a small yellow submarine, which is submerged alongside the boat.  It's  called the CHIRP. 
 
"chirp, chirp, chirp."
 
And you might think that's because of the bird like sound it emits. But actually it stands for compressed high intensity radar pulse. The CHIRP sends a signal to a computer monitor right on the boat giving the seismologists a detailed view of the complex topography under the lake. 
  
Graham Kent: "On land that field of study is called Paleoseismology. But they tend to use backhoes, and backhoes don't work so well in the water. So this CHIRP profiler is a acoustic backhoe. So as you saw out on the lake today, you get unbelievable pictures in real time of what the sediments look like and how they're warped and deformed and faulted. So we go out there and make maps to understand the history of those ruptures and that gives us a sense of when the next big one in the Tahoe Basin might occur."
 
The CHIRP profiler is helping unravel all kinds of mysteries. For instance, Kent says we now know that that the faults sometimes erupt together, creating earthquakes as large as 7.0-7.5.  And  a quake that big would mean a potentially deadly tsunami up to thirty feet high.
 
Graham Kent:  "Since I also run the Nevada Seismological laboratory, I  would be remiss to remind people that the biggest story in Japan is the fact that the number of people that didn't die, and it's because of preparedness. Ultimately, preparedness trumps everything else. If you know anything about Japan, they prepared for this day, even though the tsunami was larger than they thought, they prepared for that day, and you can see it in the YouTube videos - people by and large were on a move in a way that wouldn't happen in the U.S. today."
 
So what should you do if your Tahoe summer vacation gets interrupted by an earthquake on Lake Tahoe. Kent  recommends you duck and take cover waiting out the shaking and then, in a reasoned way get as high as you can.
 
Kent says he is working with officials in California and Nevada and hopes to see tsunami warning signs on the lake in the not too distant future.  


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