Seeing Through Rocks: Seismic Imaging of the Cascadia Subduction Zone

Now here's a pretty cool article from the PNSN blog, in which a ship of scientists go out into the Cascadia subduction zone and image the fault, right through the water, using an ingenious method:

The technology we used, called “reflection seismology,” is the sort of technology that oil companies use to search for oil reservoirs. Basically, we send seismic waves into the earth and the waves bounce off the contrasts between different rocks in the subsurface. We record these reflections with seismometers and turn them into an image, allowing us to see into the earth and study the subsurface. This can be done on land or at sea.

Here’s how we did it at sea: first we unrolled a 5-mile long “streamer” off the largest spools known to mankind and strung it out straight behind the ship. The streamer looks like a fire hose but is actually a string of seismometers spaced every couple of feet. We attached an orange “bird” to the streamer every so often that keeps the streamer at a constant depth below the water. The bird tips its wings if it gets too deep or too shallow and "flies" back to the correct depth. You can see a picture of Jackie carrying a bird over to be deployed and a bird going out on the streamer behind the boat below:

Next we deployed our seismic source, the “airguns." Each of the 36 “guns” holds 2000 psi of compressed air. To “fire,” it simply releases that air into the water. The bubble of air collapses instantly under the pressure of the water and makes a loud boom when it does. That boom generates seismic waves that propagate down through the water and into the earth, bounce off rock layers, folds, and faults, and make their way back to the streamer where we record it. Then we process this data and turn it into images.

www.pnsn.org...

Visit the article for more information, and yes...pics!

They were even kind to the dolphins and whales, carrying with them five special observers that would tell them when they spotted the animals- swarms of animals in some cases! When spotted they would stop, so as not to hurt their sensitive hearing.

A resulting image (large) from the tomography, with explanation:



Note the Y-axis is TIME, not DEPTH! And that for me makes looking at it a bit difficult to understand at first.

She says that further processing is taking place in Wyoming- which will eventually produce more easily understood images, that actually do show up as depth on the Y-axis.

It would be great if further processing, which is being done on an open access basis, and which will be available to all in a few weeks, could yield important clues into when the next rupture in Cascadia might occur. But I won't be holding my breath... Scientists have been doing this and other kinds of tomography for years and years. And yet we still don't seem to be much closer to predicting the big ones.

However, having high resolution tomographic images going into to a big quake as a baseline, so that it can be compared to the results afterwards, will no doubt yield more clues- as they can analyze where the fault ruptured and at what depths- as well as the different compositional layers of the crust and how it ruptured. So I believe it is a good thing. It may take us another 1000 years, but I believe one day, with highly resolute data like this, we might just get there. Very, very interesting, at least to me...What do you guys think?

And OH, thanks PNSN for another great article on the blog! Note that John Vidale, its Director, is a member here at ATS. Perhaps one day soon he can give some in depth commentary. After he finishes reviewing that little quake swarm off the Oregon coast, that is.

Be funny if they cause a domino effect by using that technology on that zone which causes a big quake.

Seriously i hope they thought about that

Not really likely, but our worryis noted......
Is this the same as the haaarp technology ive heard the oil cos use?
Though i understand it runs 30 watts of power not a million like the real haarp.....

reply to post by dreamfox1


Lol, umm...sorry. A measily 2000 psi air blast? Not a chance to set off a fault that big with something so small. A 7+ earthquake nearby might though.

What we should be doing with our Deep Rock Ground Penetrating Radar as well as several Military developed Deep Ground Particle Imaging Tech is finding relatively stable and safe areas to set up Geothermal Energy Producing Plants.

This form of energy production has in the past cost more money than the Energy it Generated due to poor site location as you need to go deep in a stable area to not have to be constantly replacing Heat Collection Units at ideal depths as a little shake and bake plus ground water causing explosive results can cost a company lots of money.

Geothermal Energy Production is way under used and with proper site locations...it is possible to produce Massive amounts of Energy without loosing your Heat Collecting Equipment by either explosive ground water bleeding or Super Caustic Liquids that are always present and can eat away at Multi-million dollar equipment at to quick a rate.

Geothermal Energy Generation is pitiful in it's under use...and as long as a stable site is located...Companies will be willing to build Large Scale Plants that will do something besides provide them with a Loss as well as provide Government Tax Breaks and Special Funding that comes with developing Clean Energy. Split Infinity

reply to post by dreamfox1


The chances of triggering a big earthquake are infinitesimal. One of the goals of the project is to make progress on forecasting earthquakes here, at least their rupture pattern and history if not the time of next occurrence, not to cause damage.

reply to post by TrueAmerican


Thanks for posting this. I'm actually on vacation in Oakland at the moment, not generating any interesting results.

reply to post by JohnVidale


Really, how could anyone want a vacation working in such a cool field as seismology?

Is that a pic of the PNSN control room I see with all those monitors? Or is that on the ship?

reply to post by TrueAmerican


That's onboard the ship.

Originally posted by JohnVidale
reply to post by TrueAmerican

 

That's onboard the ship.

Wow, if that's the control room on board the ship, I can only image what the control room at PNSN looks like! Come on John, give us a preview one of these days, so I can have seismogasms!

reply to post by TrueAmerican


We're not so centralized in our command center. Half the time we're working via conference call.

If this link works, it shows the console on my desk, at least
earthweb.ess.washington.edu...