26 March 2011

Shake, rattle, and roll...to scale

Last week was spring break here in Madison, WI.  It’s been a while since I took part in the annual mass exodus, but I decided to take advantage of the time off, pack up, and get out of Dodge for a few days.  My destination was chilly, drizzly Seattle for an in-person crash course about the study of earthquakes and their associated dangers in the Puget Sound area.  I also went out to meet some of the people—both professional scientists and volunteer citizens—who are helping this effort along.

Spring Break 2011!  Downtown Seattle as seen from West Seattle across Elliott Bay.
The timing of my trip during the week after Japan’s subduction-related magnitude 9.0 Tohuku earthquake and the resulting tsunami, and not long after a shallow crustal temblor hit Christchurch, NZ, was purely coincidental.  It did, however, provide an engaging, albeit tragic, backdrop for discussing earthquake hazards in the area and individual motivations for contributing to the study of these hazards.  The susceptibility of the Puget Sound to both of these types of earthquakes, as well as to large deep earthquakes such as the 2001 Nisqually quake, and the parallels to these recent events is not lost on many in the region.

I arranged the trip with the help of the staff at the Pacific Northwest Seismic Network, headquartered in the Department of Earth and Space Sciences at the University of Washington in Seattle.  For two days, I toured the area from the UW campus down to Olympia and back up to North Seattle.  My guide was Doug Gibbons, one of PNSN’s very knowledgeable technicians and an outreach specialist, who let me to pick his brain the whole time while he navigated through traffic on I-5 and many other labyrinthine routes that connect towns and neighborhoods on the Sound’s east side.

Along the way, Doug pointed out many of the local geologic features—some, like the drumlins and floodplains, that are relics of past glaciations, and others resulting from the Northwest’s particular tectonic setting—that impart the region with much of its distinct character, as well as its distinct seismic hazards.  We also stopped off to visit a number of volunteers (the subject of a longer piece on which I’m currently working) that PNSN has enlisted to broaden their post-quake data collection capacity.

Display monitors and seismographs at PNSN headquarters.
My visit was brief but chock-full of fascinating nuggets and interesting characters.  While I plan to add more posts related to this trip, I thought I’d limit this entry and just share some low-budget video I shot at PNSN’s lab.  Low budget, but awesome.  In it, Doug demonstrates and explains some of the potential threats to Seattle’s buildings and infrastructure from earthquake-related ground shaking using a “toy” shake table.

The back-and-forth motion of the shake table is powered by a motor that drives a belt and flywheel assembly, which is connected to the table's platform via a small rod.  The rate at which the platform oscillates can be regulated with a control knob for the motor to simulate seismic waves of different frequency.

In the first clip, Doug initially shows the effect of ground/soil type on shaking of two equivalent buildings.  The building at left has a rigid support, simulating bedrock or at least more solidly compacted soil, whereas the building at right is supported on foam padding, simulating the sort of less consolidated glacial till on which much of the low-lying Seattle area is constructed.  He then swaps out the first table for a second, which simulates the behavior of buildings of varying height built on similar ground.

(You might need to turn up the volume a bit. )

Cross bracing (image from Wikimedia Commons)

A couple interesting points that he makes:

1) Higher frequency waves and ground shaking don’t necessarily mean greater damage.  Lower frequency (i.e, longer period) waves may cause more damage, as shown in both simulations.  Furthermore, each building has its own resonance frequency at which shaking stabilizes and less structural damage occurs.

2) Injuries can occur regardless of how vigorously a building is shaking, or how much structural damage a building sustains.  This is because bookshelves and other unsecured objects, which shake independently of the building will still be “flying everywhere.”

In the second clip, he briefly discusses modifications and construction techniques that are used to dampen shaking and reduce structural damage.  These include adding weight, including cross braces or trusses between floors, and enlarging building footprints.

PNSN Earthquake Demo - part 2 from Timothy Oleson on Vimeo.

From what I gather, the shake table demo is usually presented to groups of children.  I’m not sure what it says about me that I really wanted to see the demo for myself.  Honestly, though, I think it is just as useful a tool for explaining the fundamental hazards for adults.  Regardless, Doug was a good sport and obliged me, and I thank him for it.

The popcorn demo.
In case you’re wondering why there is a large jar of popcorn kernels sitting on the desk in the video, it’s because it is part of another demo that he does for kids.  It’s simpler and slightly less interactive, but, he says, it’s still pretty effective.  To illustrate the logarithmic nature of the Richter scale—the common measure of an earthquake’s “size,” or the amount of energy it releases—he uses jars filled with varying numbers of kernels.

If the amount of energy released by a magnitude 1.0 earthquake, which typically produces imperceptible ground shaking, is represented by a single kernel, then a magnitude 2.0 is represented by 10 kernels, a 3.0 by 100 kernels and so on.  When he really starts blowing young minds, Doug says, is when he starts talking about large earthquakes in terms of bucketfuls and then roomfuls of kernels.

In its long-awaited return, the Awesomeness Meter rates the shake table demo as:

Finally, if you’re interested in seeing still another cool earthquake demo, head to Matt Kuchta’s blog, Research at a Snail’s Pace, to check out his “Earthquake Machine.”  He demonstrates the locking and slipping behavior of faults with a brick, a string, and some sandpaper…and, he records the data!  (Matt, incidentally, is a fellow GeoBadger who I know from my former incarnation as a geology grad student.  He is also a prolific blogger and a frequent provider of simple, yet awesome, demos on all sorts of science.  I recommend dropping in from time to time to see what contraptions he’s come up with.)


  1. Sounds like a great trip, Tim! The shake table demonstration was interesting - does that make me a kid too? :) I never considered that lower frequency can cause more damage. Do you know if builders regularly consider height of buildings when drawing up plans for various areas?

  2. Wow Tim nice post. I would almost venture to say that an "N" is in order for the awesomeness meter.

    Glad to see the emphasis on the resonant frequency of things and their effects. And so, I just found out that we here in Wisconsin live pretty close to a major fault line. Umm can you explain?

  3. Fascinating videos, Tim. I don't think the demos should be limited to kids. Visualizing frequency waves' effects on structures is extremely helpful in understanding the larger effects of an earthquake. Your videos and commentary highlight something I've never considered before -- well done!

  4. Very interesting post Tim! A science center for kids that I worked at a few years ago has a seismometer that picked up the earthquake in Japan, it might be for kids but I think we can all appreciate learning more about events like these.

  5. Interesting post, Tim! I second everyone's comments on the "awesomeness" of the demos. And I'm jealous of your trip!

  6. Wow, thanks for the all comments guys. Nice to see that my directorial debut was a success. Yeah, I maintain that demos, no matter the branch of science, are fun and useful for everyone.

    @Caroline: I can't speak with great authority, but I would certainly imagine that building height is a major consideration during design and construction. I know that the rock/soil on which a building is to sit is also a huge factor.

    @Eric: I almost added that N, yeah. Offhand, I'm not certain which fault you're referring to...possibly one having to do with the old Keweenawan Rift? That was a rift that started over a billion years ago when North America started to split apart, but then it failed. There aren't any faults in Wisconsin that have been active in recent history that I know of.

  7. Neat stuff! And thanks for the signal boost :) I like your awesome scale.

  8. Way to go, Tim - this is a terrific post. I love your demos. And the popcorn demo is a terrific way to help explain the exponential Richter scale -- I'd never thought about it that way. Makes me realize how much potential multimedia has for science journalism (for health journalism, too, I think).

  9. That's fantastic! I'm keenly interested in the volunteering you mentioned; I live in the greater Seattle area and am hoping to go back to school for geology, but I can't afford it at the moment. Anything I can do to get my hands on some geology interaction would be fantastic! I look forward to that longer piece you allude to.

  10. @steamforged: Thanks for the comment! If you're interested in the volunteer program, you can check out some information at the PNSN or USGS websites...the program is called NetQuakes. Best of luck in your geology-related endeavors!

  11. Great post, Tim! And what incredible timing as well with the tragedy in Japan. Hopefully, you'll have a lot of interested prospective publishers for your story given the interest in earthquakes within the news at this time.
    I would also say that you're never too old to enjoy things designed for kids. :)

  12. Terrific post, Tim. I really liked the use of video - I love shake tables and all those rock-rattle-roll examples used in museums. There's a couple of great ones in California Academy of Science museum, not surprisingly. And this is very well timed both to events in Japan and, I hope, to your upcoming Seattle based story.

  13. I agree that this might need an "N" on the meter. Good commitment here, especially on the destructiveness of low frequency temblors. I'm on my way to SF, and an apartment I was looking at was on Treasure Island, which is manmade, so the danger of liquefaction is high... scary!