The continents move. That fact by itself is pretty incredible. Slabs of rock thousands of miles across are sliding on a softer layer deep below the surface. In the nearly 100 years since this Continental Drift was described by German meteorologist Alfred Wegener, geologists have discovered a host of information about how they’re moving, and about the dynamics within the Earth that are driving the motion. This picture of how geologic processes function is fascinating, but in science there are always more questions. When taking pictures, resolution matters. In modern terms, the more pixels you have, the better the picture looks; and if you’re doing science, the more you can learn. In a very rough sense, that is the premise of the Earthscope project. Earthscope is an ambitious project funded by the National Science Foundation. Earthscope is deploying over 400 seismometers, 175 strain meters, and 900 GPS units to around 1600 locations around the United States. There’s even a hole being dug through the San Andreas Fault in California, a part of the project called SAFOD (which sounds like an oblique Douglas Adams reference; if so, none of their liturature cops to it). The instruments are expensive, so there’s no where near the funding to deploy enough seismometer units to cover the US at the level of detail they want (you may have noticed a little discrepancy in the numbers above). The solution is to make a smaller number of portable seismometers, and slowly leap-frog them across the country over the next decade. It’s not like the plate will be dramatically changing direction in the next 10 years.
Four years in, the project is in full swing. Nearly all the GPS units are in place, and the first wave of seismometers has already been picked up and moved to the next location. The video here is a great example of the detail obtainable by Earthscope. This is a recording of the magnitude 8.0 earthquake in Sumatra on September 12th, 2007. The map shows the amplitude of the seismometer reading at each seismic station. You can see the waves moving across the array. What’s very cool, though, is that at about the 40 second mark you’ll see the waves start to move the other way! Those are the waves that traveled the long way around the Earth from Sumatra. It reverses again near the end to show the first wave having come all the way around again. (The youtube video is a bit low resolution. Here is the hi-res version, and more videos are here.)
The seismometers are only part of the story, though. The GPS units provide incredibly precise data on the exact location of each station. So precise, in fact, that over only a short time they can detect the motion of the continental drift, and measure differences between the motion at nearby stations. This allows the geologists to map in detail how the North American plate is moving; not only the motion relative to the other plates, but also how it’s stretching and bending — how much strain it receives from interacting with nearby plates. From the Earthscope website, this array is capable of addressing questions such as:
- What controls the space-time pattern of earthquake occurrence?
- How do earthquakes nucleate?
- What are the dynamics of magma rise, intrusion, and eruption?
- How can we reduce the hazards of earthquakes and volcanic eruptions?
Via Kim Hannula of All of My Faults Are Stress-Related, it turns out you can explore the GPS data in Google Earth. She points out some of the features you can explore, such as the 3 dimensional motion near Mount St. Helens seen here, which is currently sinking and spreading out a bit.
This has only touched the surface of the science being produced at Earthscope. The full project will take another decade to complete, and like all big science projects should produce some interesting surprises. For more information, see the Earthscope website. (Note that this is earthscope.org, earthscope.com is a different project entirely.)